migrateAccount.php: allow --attachmissing and --attachbroken together

No reason for the two to be mutually exclusive, a same list of
usernames can be used for both. Also, having a global account is
either expected or a normal step in the process, always tell as info.

Change-Id: I6a06d8a869c9b77260316f5397861d79b36f2d83
Merge "migrateAccount.php: allow --attachmissing and --attachbroken together"