[telemetry] Make --android-rndis enable adb root access automatically rather
than prompt the user to figure it out and do it.

Review URL: https://codereview.chromium.org/26116005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228241 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228241