Update manifests to point to specific snappy commit

We will be changing the name of the old master branch to
old-master. As a result we need to make sure snappy revisions
are explicitly defined.

Change-Id: I31ffa263761a420fd2abd116ba4f62bbb58fe484
Reviewed-on: http://review.couchbase.org/30648
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>