Allow cipd manifest file to contain package name templates.

Allow cipd ensure file to contain package name templates.

This will allow ensure files to be generically specified regardless of
platform, e.g.

  path/to/package/${platform}  git_revision:deadbeef....

R=dnj@chromium.org, vadimsh@chromium.org
BUG=663843
Committed: https://github.com/luci/luci-go/commit/307e15deab37650e9627fe3d06ee88a2dd82e1cd

[Vadim Sh., 2016-12-08 21:05:55]

lgtm with nits:
1. Change "manifest file" in CL description to "ensure file". "Manifest file" is
a thing inside the zip package, not the thing passed to 'ensure'.
2. Add a tiny test.

[iannucci, 2016-12-08 22:27:13]

Description was changed from

==========
Allow cipd manifest file to contain package name templates.

This will allow manifest files to be generically specified regardless of
platform, e.g.

  path/to/package/${platform}  git_revision:deadbeef....

R=dnj@chromium.org, vadimsh@chromium.org
BUG=663843
==========

to

==========
Allow cipd ensure file to contain package name templates.

This will allow ensure files to be generically specified regardless of
platform, e.g.

  path/to/package/${platform}  git_revision:deadbeef....

R=dnj@chromium.org, vadimsh@chromium.org
BUG=663843
==========

[iannucci, 2016-12-09 01:15:49]

done

[iannucci, 2016-12-09 03:56:04]

The CQ bit was checked by iannucci@chromium.org

[iannucci, 2016-12-09 03:56:04]

The patchset sent to the CQ was uploaded after l-g-t-m from vadimsh@chromium.org
Link to the patchset: https://codereview.chromium.org/2559893003/#ps20001
(title: "Add test")

[commit-bot: I haz the power, 2016-12-09 03:56:10]

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, 2016-12-09 04:04:49]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1481255764025950,
"parent_rev": "97589d3020d8457413b89469f1f1fa59cc48120e", "commit_rev":
"307e15deab37650e9627fe3d06ee88a2dd82e1cd"}

[commit-bot: I haz the power, 2016-12-09 04:04:51]

Description was changed from

==========
Allow cipd ensure file to contain package name templates.

This will allow ensure files to be generically specified regardless of
platform, e.g.

  path/to/package/${platform}  git_revision:deadbeef....

R=dnj@chromium.org, vadimsh@chromium.org
BUG=663843
==========

to

==========
Allow cipd ensure file to contain package name templates.

This will allow ensure files to be generically specified regardless of
platform, e.g.

  path/to/package/${platform}  git_revision:deadbeef....

R=dnj@chromium.org, vadimsh@chromium.org
BUG=663843

Committed:
https://github.com/luci/luci-go/commit/307e15deab37650e9627fe3d06ee88a2dd82e1cd
==========

[commit-bot: I haz the power, 2016-12-09 04:04:52]

Committed patchset #2 (id:20001) as
https://github.com/luci/luci-go/commit/307e15deab37650e9627fe3d06ee88a2dd82e1cd