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: I706f381e0e51bab204bae35aa9a634dad499b081
Implements: blueprint use-data-bag-for-qpid-password
Merge "Use get_password method to obtain qpid password"