Allow kwargs in create_server_snapshot

As a part of the scenario/manager.py stabilization tracked by
the below BP the patch adds kwargs argument for create_server_snapshot
method so that the consumers are able to pass additional
parameters if needed.

Implements: blueprint tempest-scenario-manager-stable

Change-Id: I0ae3f86c546be6b3f5b1d427568cfdf2d26e37e0
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index ff860d5..a878aef 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -649,7 +649,7 @@
         if not isinstance(exc, lib_exc.SSHTimeout):
             LOG.debug('Network information on a devstack host')
 
-    def create_server_snapshot(self, server, name=None):
+    def create_server_snapshot(self, server, name=None, **kwargs):
         """Creates server snapshot"""
         # Glance client
         _image_client = self.image_client
@@ -658,7 +658,7 @@
         if name is None:
             name = data_utils.rand_name(self.__class__.__name__ + 'snapshot')
         LOG.debug("Creating a snapshot image for server: %s", server['name'])
-        image = _images_client.create_image(server['id'], name=name)
+        image = _images_client.create_image(server['id'], name=name, **kwargs)
         image_id = image.response['location'].split('images/')[1]
         waiters.wait_for_image_status(_image_client, image_id, 'active')