Access policy editor: adding non-exist user should not display internal server error

Change-Id: Ibb7ea8a115cc366825b53cc796b085a6b79041d2
added bug 999391 to release notes for 0.16.2

Change-Id: I031249ee8955e76b70c73e507c9f2b9a738bcb98
Allow removal of groups with existing access policy rule

Bug: 1085703
Change-Id: I9984a13594866ccb19ade9a0a2e6b8d88a8003f9
Merge branch 'release-0.16' into develop