Refactor password validity checking

Refactor the password checks to return a status object, so the function
can handle the entire error message, or return multiple error messages.

This patchset aims to keep the functionality identical. A followup
patchset can further improve the functionality. E.g., although
getPasswordValidity stated it could return an array of messages, it
never did so except from the hook, so most callers expect and handle a
single string.

Change-Id: I87644486f5572dc067ebdbacd01fb39c67e5612a
Merge "Refactor password validity checking"