cros: Wait for auto enrollment check before enabling kiosk.

Kiosk enabling should only be used when auto enrollment is not going to be
enforced. So that it is not used as a way to bypass auto enrollment.

BUG=309780
TEST=KioskTest.KioskEnableAbortedWithAutoEnrollment

Review URL: https://codereview.chromium.org/31063006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230766 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230766