Add rule for list_groups_for_user in policy.json

Providing an initial policy rule for the list_groups_for_user
operation in the sample policy.json file for the ease of
configuration.

Fixes bug #1167836

Change-Id: Id253729098a95d3b129babde1b3706f409a095dd
Merge "Add rule for list_groups_for_user in policy.json"