Don't start or stop if COUCHDB_NO_START is set

The JavaScript test runner should not try to start or stop
the CouchDB instance with ./utils/run when COUCHDB_NO_START
is set.
Make JS test runner work with single file

Commit 9dfddaa7bf30d30c8fbbc4e1cc2bff4dc35dadac broke running
the JavaScript test runner with a single file. It just did
not run the test.