Adding support for crossdomain middleware: the entry is
multiline string which is the full value for cross_domain_policy key of proxy-server.conf
See http://docs.openstack.org/developer/swift/crossdomain.html
added primitive check for cross_domain_policy value validation
Merge pull request #252 from jsuchome/crossdomain_middleware

Adding support for crossdomain middleware
Show a conflict message when ceph-radosgw is already deployed
allow saving conflicting proposal
Merge pull request #255 from jsuchome/conflict_with_ceph

raise a conflict when ceph-radosgw is already deployed