Make default key_filter callback replace . and : found in key names to _

This makes statsd happier and makes graphite hierarchies make more sense.

Change-Id: I56169743198a1619ca549185a06860e586116c32
Fix bug where metric_name would be prefixed and suffixed multiple times when using multiple outputs

Change-Id: I8ba2141753724244854080b2bebcfa8105439480
Merge remote-tracking branch 'origin/master' into debian