Googlers should be able to tell the buildbot to launch builds for an
external contributor's change, but Gerrit is determined to make this
hard for us. The email sent by Gerrit for comments doesn't actually
contain the email address of the commenter in any clear way, only the
name. It does however contain a list of `Gerrit-Reviewer: Name
<email>` entries that could be used for this though.
Change-Id: Iee61f06dcd8f0024f16b535ea9a34765bf01b2e7
29be129342