Change method to get the user_id

Instead of "find_project", using "find_user" to get the user_id
while the option --user is specified for "openstack volume list"

Change-Id: Iea8472b7b8e709a8792a56575e00003a9cbdaa39
Closes-Bug: #1514145

Author: simenhhu

openstackclient/volume/v2/volume.py

@@ -304,9 +304,9 @@ def _format_attach(attachments):
 
         user_id = None
         if parsed_args.user:
-            user_id = identity_common.find_project(identity_client,
-                                                   parsed_args.user,
-                                                   parsed_args.user_domain)
+            user_id = identity_common.find_user(identity_client,
+                                                parsed_args.user,
+                                                parsed_args.user_domain)
 
         search_opts = {
             'all_tenants': parsed_args.all_projects,