Update Gerrit and LAVA integration

Notes:
[pfefferz, 9/16/2011] While we're in here, I'd like to see what we can do about solving the mega upgrade work flow. It goes like this:

1. The maintainer pushes a huge upgrade
2. The upgrade breaks the mainline
3. We fix the upgrade

What would be great is:

1. Maintainer pushes to a test branch
2. Test branch is autotested
3. Maintainer fixes issue
4. On success the whole mega patch set is applied

[fgiff, 20110923] Postponing items that are enhancements we don't strictly needed for this cycle.

[pfefferz, 2011/10/03] Filed https://blueprints.launchpad.net/linaro-android/+spec/linaro-android-enhance-gerrit-and-lava-integration to track POSTPONED items that are enhancements to the core functionality.

Headline:
Automated verification and merge of changes reviewed in gerrit.

Acceptance:
Changes reviewed in gerrit are automatically built and tested. Changes that successfully build and pass testing are automatically marked as verified and merged.

Work items:
Check for build submission success: DONE
Use build jobs owned by gerrit-bot: DONE
Handle non-availability of servers: DONE
Build/test multiple jobs: DONE
Handle manifest changes: DONE
Check that review branch and build job branch are compatible: DONE
Only test device-specific changes on that device: DONE
Remove duplicate build comments: DONE
Don't build the same patchset more than once: DONE
Ensure we pull the correct build number when there are queued builds: DONE
Delay commenting until each board result is available: DONE
Remove hard-coded parameters: DONE
Improve exception handling: DONE
Move state from files to a database: DONE
Refactor code to eliminate duplicate functionality: DONE