Pass through nova region name

If the region name is specified in the config, we need to pass it
in to the nova client constructor. Since key_name is similarly optional,
go ahead and handle both parameters the same.

cloud/nova_compute

@@ -308,13 +308,14 @@ def _create_server(module, nova):
     bootkwargs = {
                 'nics' : module.params['nics'],
                 'meta' : module.params['meta'],
-                'key_name': module.params['key_name'],
                 'security_groups': module.params['security_groups'].split(','),
                 #userdata is unhyphenated in novaclient, but hyphenated here for consistency with the ec2 module:
                 'userdata': module.params['user_data'],
     }
-    if not module.params['key_name']:
-        del bootkwargs['key_name']
+
+    for optional_param in ('region_name', 'key_name'):
+        if module.params[optional_param]:
+            bootkwargs[optional_param] = module.params[optional_param]
     try:
         server = nova.servers.create(*bootargs, **bootkwargs)
         server = nova.servers.get(server.id)