Prepend jinja2 path for hermeticity.

Prepend jinja2 path for hermeticity.

On systems with an older local install, appending the third_party path to
jinja2 will result in the local install being used.
Switching to prepending to avoid this.

BUG=470543
TEST=local
R=ncbray@chromium.org,jamesr@chromium.org

Committed: https://crrev.com/455590124cbf51420078e8230f4d03aaf20fa492
Cr-Commit-Position: refs/heads/master@{#322712}

[Nick Bray (chromium), 2015-03-25 18:24:38]

LGTM, just make sure to rebase and retry due to the time lag.

[Nick Bray (chromium), 2015-03-25 18:25:58]

FYI for the mojo OWNERS: this script is deprecated and we'll switch over to the
checked-in sources soon, but I want to keep this in place because I need to do a
breaking change to the checked-in sources.  Patching this script is fine.

[bradn, 2015-03-25 18:44:46]

The CQ bit was checked by bradnelson@google.com

[bradn, 2015-03-25 18:44:46]

The patchset sent to the CQ was uploaded after l-g-t-m from ncbray@chromium.org
Link to the patchset: https://codereview.chromium.org/813483005/#ps20001 (title:
"merge")

[commit-bot: I haz the power, 2015-03-25 18:46:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/813483005/20001

[commit-bot: I haz the power, 2015-03-25 19:00:53]

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

[commit-bot: I haz the power, 2015-03-25 19:00:54]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[tfarina, 2015-03-28 19:24:50]

tfarina@chromium.org changed reviewers:
+ jamesr@chromium.org

[tfarina, 2015-03-28 19:24:51]

James, could you approve this? I'm still being hit by this.

[jamesr, 2015-03-28 22:26:22]

lgtm

[tfarina, 2015-03-28 22:33:07]

Thanks, I'm checking the cq box.

[tfarina, 2015-03-28 22:33:20]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-03-28 22:33:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/813483005/20001

[commit-bot: I haz the power, 2015-03-28 23:20:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-28 23:21:19]

Patchset 2 (id:??) landed as
https://crrev.com/455590124cbf51420078e8230f4d03aaf20fa492
Cr-Commit-Position: refs/heads/master@{#322712}