Fail hard if OpenSSL isn't found

Change-Id: Icd8fcac4dffe81c192f3a216ac344d190139805a
Reviewed-on: http://review.couchbase.org/33244
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>