Fix keystone password update for users

keystone-client changed its error message when an invalid
password is specified. The logic is updated so that puppet
can update passwords for users.

Backport of I090f7e2ee62ee189f37921c091fe51b6d587cd74

Change-Id: I049bd99b9474204ff498863095beb8eecc641aee
Partial-Bug: #1400701
Merge "Fix keystone password update for users" into stable/6.0