Point graphite CNAME at tungsten in eqiad

* tungsten is the new Graphite host in eqiad, replacing professor in pmtpa.
* Set graphite CNAME TTL to 600
* Drop gdash and graphite wmnet CNAMEs.

Change-Id: If02fec8505389fc6a23cd5c79f39d63fd892c669
Merge "Point graphite CNAME at tungsten in eqiad"