Update git submodules

* Update charm-glance-simplestreams-sync from branch 'master'
  - Drop RabbitMQ support
    
    Drop support for sending sync status messages to a RMQ exchange.
    
    This was used by conjure-up which is no longer maintained so
    drop the supporting code, metadata and options and remove
    RabbitMQ from all test bundles.
    
    Change-Id: I504508a64e50a9d331f6c5d69b292d9ccc20da3d
    Func-Test-PR: openstack-charmers/zaza-openstack-tests#321