core : Remove manipulating instance VM action group from role UserInstanceManager

Role UserInstanceManager has manipulating instance VM action group, but there is no such action in UserPortal.
This patch removes the action group from the role.

Change-Id: Ie01408cc4c2f9d7de87abfb5e8500dc112dfb23c
Bug-Url: https://bugzilla.redhat.com/1072773
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>