MB-11293: Fix paths to erts

We seem to assume a specific major version of Erlang in the script
which causes trouble every time. Make it use erts-* as we will
(ought to) have only one version of ERTS at any given time.

Change-Id: Ie4d6434ac554f460b7c2b3a6de83e71ad6387f8e
Reviewed-on: http://review.couchbase.org/37899
Tested-by: Sriram Melkote <siri@couchbase.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>