Throw an exception if password hash would be truncated by DB

Throw an exception if password hash would be truncated by DB

DB uses a tinyblob field. With layered encrypted passwords, the
length gets close to 255 and can exceed if you use a long name
for the password type. Previously these would be silently inserted
into the DB and truncated, which would lock user out of their
account.

Change-Id: Idf0d0248b181f42d92e3ad6c3220b5331cd4d4d0