Add change kind to PatchSetCreatedEvent

Pass along an extra flag in the patchset-created hook to convey
the change kind.  This is also exposed in the PatchSetCreatedEvent
as the "kind" field.  Both follow the ChangeKind enum type, where a
change can be "REWORK", "NO_CODE_CHANGE", or "TRIVIAL_REBASE".

Bug: Issue 2634
Change-Id: Ie04d0282e42ab177810fafd857e90d21999cab28
6 files changed