Revert of Track step nesting in StreamEngine.

Revert of Track step nesting in StreamEngine. (patchset #5 id:80001 of https://codereview.chromium.org/2245113002/ )

Reason for revert:
Broke a build: https://uberchromegw.corp.google.com/i/internal.infra.cron/builders/recipe-autoroller-internal/builds/18474/steps/build.roll/logs/candidate%20%233

Original issue's description:
> Track step nesting in StreamEngine.
> 
> Currently, step nesting is tracked by the step runner as an integer,
> which is passed to the stream engine as the `set_nest_level` post-create
> event. This poses two problems, namely:
> - The nest level is known to the runner immediately on step creation,
>   but is presented to the stream engine as a separate piece of
>   information.
> - This forces the step runner's concept of nesting (integer) onto the
>   stream engine, when all it really cares about is whether or not a step
>   is nested.
> 
> This patch updates the API to pass the nested state as a boolean: either
> a step is nested in the previous step, or it isn't. The stream engine is
> responsible for tracking how it represents this to the stream's
> consumer. The nested state is also passed at step creation, making
> nesting an atomic step propety instead of an out-of-band option.
> 
> Along the way, small cleanups.
> 
> BUG=chromium:628770
> TEST=local
>   - Ran unit tests locally.
>   - `./recipes.py --package ./infra/config/recipes.cfg run example/nested`
> 
> Committed: https://github.com/luci/recipes-py/commit/4b3ff6014bcb018aff9ae2755faf47cc304f47af

TBR=martiniss@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:628770
Committed: https://github.com/luci/recipes-py/commit/339eace18cba35868b8bbb039100448fbfc58d15

[dnj, 2016-09-08 19:11:52]

The CQ bit was checked by dnj@chromium.org

[dnj, 2016-09-08 19:11:52]

Created Revert of Track step nesting in StreamEngine.

[commit-bot: I haz the power, 2016-09-08 19:12:02]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-08 19:12:16]

Description was changed from

==========
Revert of Track step nesting in StreamEngine. (patchset #5 id:80001 of
https://codereview.chromium.org/2245113002/ )

Reason for revert:
Broke a build:
https://uberchromegw.corp.google.com/i/internal.infra.cron/builders/recipe-au...

Original issue's description:
> Track step nesting in StreamEngine.
> 
> Currently, step nesting is tracked by the step runner as an integer,
> which is passed to the stream engine as the `set_nest_level` post-create
> event. This poses two problems, namely:
> - The nest level is known to the runner immediately on step creation,
>   but is presented to the stream engine as a separate piece of
>   information.
> - This forces the step runner's concept of nesting (integer) onto the
>   stream engine, when all it really cares about is whether or not a step
>   is nested.
> 
> This patch updates the API to pass the nested state as a boolean: either
> a step is nested in the previous step, or it isn't. The stream engine is
> responsible for tracking how it represents this to the stream's
> consumer. The nested state is also passed at step creation, making
> nesting an atomic step propety instead of an out-of-band option.
> 
> Along the way, small cleanups.
> 
> BUG=chromium:628770
> TEST=local
>   - Ran unit tests locally.
>   - `./recipes.py --package ./infra/config/recipes.cfg run example/nested`
> 
> Committed:
https://github.com/luci/recipes-py/commit/4b3ff6014bcb018aff9ae2755faf47cc304...

TBR=martiniss@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:628770
==========

to

==========
Revert of Track step nesting in StreamEngine. (patchset #5 id:80001 of
https://codereview.chromium.org/2245113002/ )

Reason for revert:
Broke a build:
https://uberchromegw.corp.google.com/i/internal.infra.cron/builders/recipe-au...

Original issue's description:
> Track step nesting in StreamEngine.
> 
> Currently, step nesting is tracked by the step runner as an integer,
> which is passed to the stream engine as the `set_nest_level` post-create
> event. This poses two problems, namely:
> - The nest level is known to the runner immediately on step creation,
>   but is presented to the stream engine as a separate piece of
>   information.
> - This forces the step runner's concept of nesting (integer) onto the
>   stream engine, when all it really cares about is whether or not a step
>   is nested.
> 
> This patch updates the API to pass the nested state as a boolean: either
> a step is nested in the previous step, or it isn't. The stream engine is
> responsible for tracking how it represents this to the stream's
> consumer. The nested state is also passed at step creation, making
> nesting an atomic step propety instead of an out-of-band option.
> 
> Along the way, small cleanups.
> 
> BUG=chromium:628770
> TEST=local
>   - Ran unit tests locally.
>   - `./recipes.py --package ./infra/config/recipes.cfg run example/nested`
> 
> Committed:
https://github.com/luci/recipes-py/commit/4b3ff6014bcb018aff9ae2755faf47cc304...

TBR=martiniss@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:628770

Committed:
https://github.com/luci/recipes-py/commit/339eace18cba35868b8bbb039100448fbfc...
==========

[commit-bot: I haz the power, 2016-09-08 19:12:17]

Committed patchset #1 (id:1) as
https://github.com/luci/recipes-py/commit/339eace18cba35868b8bbb039100448fbfc...