Make battor_wrapper use target_platform instead of sys.platform

Make battor_wrapper use target_platform instead of sys.platform

This fixes a bug where trying to fetch the battor_agent while running
unit tests was resulting in an error because cloud storage access is
prohibited during Telemetry unit tests. The fetch should have resulted
in no cloud storage access because the binary should have been
prefetched, but didn't because we were using sys.platform ('linux2')
instead of target_platform ('linux').

This bug was blocking TracingControllerTest.testBattorTracing from being
reenabled, so we also reenable that in this CL.

BUG=chromium:673671

[charliea (OOO until 10-5), 2016-12-29 19:19:14]

The CQ bit was checked by charliea@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-12-29 19:19:19]

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

[charliea (OOO until 10-5), 2016-12-29 19:21:01]

Description was changed from

==========
Make battor_wrapper use target_platform instead of sys.platform

This was blocking TracingControllerTest.testBattorTracing from being
reenabled, so we also reenable that in this CL.

BUG=chromium:673671
==========

to

==========
Make battor_wrapper use target_platform instead of sys.platform

This fixes a bug where trying to fetch the battor_agent while running
unit tests was resulting in an error because cloud storage access is
prohibited during Telemetry unit tests. The fetch should have resulted
in no cloud storage access because the binary should have been
prefetched, but didn't because we were using sys.platform ('linux2')
instead of target_platform ('linux').

This bug was blocking TracingControllerTest.testBattorTracing from being
reenabled, so we also reenable that in this CL.

BUG=chromium:673671
==========

[commit-bot: I haz the power, 2016-12-29 19:37:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-12-29 19:37:49]

Dry run: This issue passed the CQ dry run.

[charliea (OOO until 10-5), 2016-12-29 19:54:25]

charliea@chromium.org changed reviewers:
+ nednguyen@google.com

[charliea (OOO until 10-5), 2017-01-05 20:55:09]

/bump

[nednguyen, 2017-01-05 21:15:15]

https://codereview.chromium.org/2608773002/diff/1/common/battor/battor/battor...
File common/battor/battor/battor_wrapper.py (right):

https://codereview.chromium.org/2608773002/diff/1/common/battor/battor/battor...
common/battor/battor/battor_wrapper.py:122: 'battor_agent_binary', '%s_%s' %
(target_platform, platform.machine()))
As said offline, this is a problem. We are using target_platform from the user
but using platform.machine() which is our logic. So theoretically, you can have:
target_platform = "Android"
platform.machine() = "x64"

And this combination doesn't make sense. So either:
1) The callsite needs to pass target_platform & target_archiecture
2) battor_wrapper is for managing binary on host machine only, it it will infer
the correct platform itself. In that case, the fix is as simple as converting
the variances of "linux", "linux2", "linux3"... to just the canonical form.