Remove improper exc handling in is_user_in_group
Remove improper exc handling in is_user_in_group

Since we are already catching the expected exceptions for that operation
there is no need to catch Exception in that method. Also, the message
was saying "error in adding user to group", but that method is just
checking ...

Change-Id: I3b6fb28773a6c52b223bca4964dba4ccc27f9787

openstack-infra/shade,stackforge/python-openstacksdk,openstack/python-openstacksdk,dtroyer/python-openstacksdk,dtroyer/python-openstacksdk,openstack-infra/shade,openstack/python-openstacksdk,stackforge/python-openstacksdk