The hash returned by the request method of Puppet::Provider::Openstack
uses symbols instead of strings as keys, see [1].
This prepends the missing ':' in front of the 'auth.auth_url' key to
make it a symbol and to have it return the actual value instead of
always coming back empty.
[1] a1dfd6861f/lib/puppet/provider/openstack.rb (L123)
Closes-Bug: #2010894
Change-Id: I97546a1030559d1f91030a668106e220ce7a7650