Installer: Validate password against sysop/bureaucrat policies

Installer: Validate password against sysop/bureaucrat policies

Previously, user-group-specific policies were not checked, because the
user hadn't been created yet, and so wasn't assigned to any groups. In his
overhaul of password policy, Chris wrote a function that was designed for
exactly this purpose (UserPasswordPolicy::checkUserPasswordForGroups) but
didn't put it into use.

Some changes to the error handling code are needed so the error messages
display correctly.

Bug: T115700
Change-Id: I1391c77c9667b646b29003bb0b2abcdc21d8c4d8