Implemented more fine-grained authentication for services

Added variables to devstack setup scripts to allow different passwords (Both DB and keystone) and DB username to be set for the core openstack services. (I.e. Keystone, Nova, Neutron, Glance, Heat, Ceilometer) The additional setup scripts (E.g. ironic, opendaylight etc.) all default back to the default DATABASE_USER and DATABASE_PASSWORD.