Switch to Gerrit as git hosting and review system

Headline:
Android team switched to Gerrit as the primary git repository hosting and review system.

Acceptance:
All manifests point to Gerrit git's and team uses Gerrit-based workflow.

Now we use always-fresh AOSP components and manually update Linaro components, how to set up it on common server? - We want to automatically update our mirror from upstream.

Work items:
Have anon git-daemon installed on android.git.linaro.org (RT ticket): DONE
Have gitweb installed on android.git.linaro.org (RT ticket): DONE
Resolve situation with android/platform/hardware/libhardware.git repository: DONE
Create "Developers" group in Gerrit, git to it permissions equivalent of those people had on git.linaro.org, assign all Android team members to it: DONE
Update manifests to point to android.git.linaro.org (can do it in the branch in parallel. Actually, can't - cannot even check out stuff out of Gerrit, anon git is required for that): DONE
Set up mirroring procedure for android.git.linaro.org: DONE
Revamp master branches for toolchain/* to be AOSP upstream syncable: DONE
Set up automated AOSP syncing (security): BLOCKED
Disable write access to git.linaro.org/android/ (chmod -w it for example): DONE
Update build configs for new manifest location: DONE
Update wiki docs for new manifest location: DONE
Enable repo download link in Gerrit UI (RT): DONE
Enable https://launchpad.net/~ OpenIDs as trusted (RT): DONE