Without this, it's really hard for operators to feel comfortable
removing support for now-deprecated digests.
This patch adds new statsd metrics in the form of:
formpost.digests.<digest>
tempurl.digest.<digest>
Something like:
formpost.digessts.sha1
tempurl.digests.sha512
Change-Id: I203607a0576582330241172d05bf8fd223bbbb9d