test: fix the unreliable no-MX record test
test: fix the unreliable no-MX record test

- it's ok to return Error.NoSuchRecord when looking for an MX record
  which doesn't exist (although it's odd that the system API doesn't
  do this consistently)
- it's ok to return a list of other records (typically CNAMEs) when
  looking for an MX record which doesn't exist (although it's odd
  that the system API doesn't do this consistently either)

Perhaps we should add some filtering to the OCaml API and hide some of
this strange detail. This patch makes the test case more tolerant.

Signed-off-by: David Scott <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@recoil.org>

djs55/ocaml-osx-dnssd