Allow kwargs in image_create

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

Change-Id: I484b3e93c25da297703835d146f91f5bcb50626f
Implements: blueprint tempest-scenario-manager-stable
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index ff860d5..fdb718d 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -573,7 +573,7 @@
         linux_client.validate_authentication()
         return linux_client
 
-    def image_create(self, name='scenario-img'):
+    def image_create(self, name='scenario-img', **kwargs):
         img_path = CONF.scenario.img_file
         if not os.path.exists(img_path):
             # TODO(kopecmartin): replace LOG.warning for rasing
@@ -613,6 +613,7 @@
             # Additional properties are flattened out in the v2 API.
             if img_properties:
                 params.update(img_properties)
+        params.update(kwargs)
         body = self.image_client.create_image(**params)
         image = body['image'] if 'image' in body else body
         self.addCleanup(self.image_client.delete_image, image['id'])