Add new hook flags for gerrit 2.5

Currently, the flags do nothing, except allow gerrit 2.5 to use
update-bugs again.

Change-Id: If6e17766bd5719af7739c546bbb764e2f797c601
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>
Merge "Add new hook flags for gerrit 2.5"