Small fix to addconfig in statsd.

AddConfiguration now returns false if the incoming byte array can't
even be parsed into the expected proto format. Unfortunately, we
can't fully evaluate if this configuration is valid. Still, this
gives the caller a chance to know that the parameters it sent can't
even be parsed.

Test: Tested that statsd still builds.
Change-Id: I7ba7c64adc4bc77549d5e9133e212a4870645786