CBD-946:  add missing modules (e.g. snappy), this time to override.xml

Change-Id: Id021ca316be60fb2b6aa667c92d19aad313025c0
Reviewed-on: http://review.couchbase.org/26826
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>