resourceloader: Use increment() for resourceloader_cache miss metric

resourceloader: Use increment() for resourceloader_cache miss metric

This makes it consistent with how we handle the resourceloader_cache hit metric.

When I added the miss metric I figured it was nice to get both counts and timings
in a single metric, but I can't trust StatsD/Graphite not to screw this up so
let's untangle them to be sure.

Change-Id: I24f68e34a9fa491806fdb6023bdd757f6688c2ed