In git version 2.4 the git branch command prints "* (HEAD detached at"
or "* (HEAD detached from" instead of "* (detached from". Adjust the parsing to make our tests
still work with git 2.4.

BUG=487172

Review URL: https://codereview.chromium.org/1162763003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295578 0039d316-1c4b-4281-b951-d872f2087c98