Central login check should fail if local is unattached

The central login check wasn't checking whether the local account is
attached when finishing up the check. The main consequence of this is
that the p-personal bar was being replaced with the local user's bar
even though the global user isn't actually logged in. Also CentralLogin
cookies were being set even though they would later be ignored/reset due
to the local account being unattached.

Bug: 51603
Change-Id: I14041651e8b1915729e3ef462f4072ff91f0ba70