Add the chroot creator to the default set of allowed groups (with override flag).
Add the chroot creator to the default set of allowed groups (with override flag).

This fixes a buildbot issue where chroots can't be used without sudo (because there is no 'admin' group, and chrome-bot only belongs to the 'chrome-bot' group).

Review URL: http://codereview.chromium.org/3755010

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@62790 0039d316-1c4b-4281-b951-d872f2087c98

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