Add marconi support to devstack

Marconi has an optional dependency on keystone for authentication. This
code was tested with everything enabled and also with the following
localrc:

    STACK_USER=fedora
    SERVICE_TOKEN=secrete
    ADMIN_PASSWORD=secrete
    MYSQL_PASSWORD=secrete
    RABBIT_PASSWORD=secrete
    SERVICE_PASSWORD=secrete

    disable_all_services
    enable_service qpid
    enable_service key
    enable_service mysql
    enable_service marconi-server

Implements blueprint marconi-devstack-integration
Implements blueprint devstack-support

Change-Id: I13495bcc5c5eb66cee641894e9f84a0089460c8b
Merge "Add marconi support to devstack"