statsd: fix flush() scheduling
statsd: fix flush() scheduling

Currently, flush() is scheduled only _once_. Indeed, loop.call_later()
is not "recursive", as it does not reschedule every flush_delay seconds
the call. It only does it once!
So let's build a closure that reschedule itself each time.

Change-Id: I2e16101890996a51cb2baa4ae7b21dd6d1e3c801

leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi