CBLT-181:  root the doc zipfile in a dir named for the build number

Change-Id: I76a95283d38cd3e5d32e2a9afa9c17d96656f2b3
Reviewed-on: http://review.couchbase.org/34402
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>