S3 devices should not be rebooted in provision step.

Rebooting s3 devices causes device to be flaky during the deploy step. This is
likely because WaitForPackageManager() does not wait long enough on the s3
devices. I've verified locally on the bot that without the reboot in the
provision step, the devices are more reliable (i.e. deploy step passes).

BUG=321063
TBR=frankf@chromium.org

Review URL: https://codereview.chromium.org/122313008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243542 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243542