Update FindCouchbaseErlang.cmake to latest from tlm

Change-Id: Ida715df99c94080fa8d2fcf9a61035317a5981ba
Reviewed-on: http://review.couchbase.org/37379
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>