Add temporary PTR record for mail.tools.wmflabs.org

PTR records for public IPs should be handled dynamically by labs-ns0.
However, we need an interim solution for the Tools mail server as many
other mail servers reject mail from a server with no PTR record.

The old PTR record for the pmtpa Tools mail server (208.80.153.183)
can be removed.

Bug: 51359
Bug: 62887
Change-Id: I16b7673e907550f7d9777f536706878183df4b7c
Merge "Add temporary PTR record for mail.tools.wmflabs.org"