Use get_password method to obtain qpid password

Currently, qpid's password is stored in an attribute in the common
cookbook.  This change causes the password to be looked up via
get_password method, which is how we obtain the rabbitmq password.

Change-Id: Id09820dafc67910f9f4d6c350ece6fe93fb21787
Implements: blueprint use-data-bag-for-qpid-password
Merge "Use get_password method to obtain qpid password"