Fix distinguishing between stack-create and stack-update

Fix distinguishing between stack-create and stack-update

Previously we tried to use UpdateIdentifier for two different things:
tell whether to perform package update, and also to tell whether the
top-level stack is being created or updated (which was incorrect and
resulted in bug 1567384, and an attempt to work around that bug resulted
in bug 1567385).

We cannot use Heat's "action" conditionals in some cases, because they
refer to the direct parent stack, which can yield undesirable results
when introducing new nested stacks or temporarily no-opping something
and then adding it back (in both these cases, "action" would be
considered "CREATE", even though the top-level stack is in "UPDATE").

So tripleoclient passes a new parameter StackAction to tell whether the
top-level stack is being created or updated, and we make use of
that. (It seems there's no better way of getting this info from within
the nested Heat stacks.)

Change-Id: Ie14ddbff15e7ed21aaa3fcdacf36e0040f912382
Depends-On: I9dc3b4cd8a6a71df34d8babf0e4c6505041f5311
Closes-Bug: #1567384
Related-Bug: #1567385