Fix access to configs hash symbol in get_auth_endpoint

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
(cherry picked from commit 5a6378c6df)

lib/puppet/provider/keystone.rb

@@ -14,7 +14,7 @@ class Puppet::Provider::Keystone < Puppet::Provider::Openstack
 
   def self.get_auth_endpoint
     configs = self.request('configuration', 'show')
-    "#{configs['auth.auth_url']}"
+    "#{configs[:'auth.auth_url']}"
   rescue Puppet::Error::OpenstackAuthInputError
     nil
   end