Partial Config Update: store metric/state hashes

Store metric and state hashes, for use when determining if the
metric/state changed.

Metric hashes include any metric activations, if present. The hash is
calculated by doing h(h(metric) | h(activation)).

Also added a getType function for metrics, since the metric will be
different if either the type, the hash, or any dependencies change.

Test: m statsd
Change-Id: I7184fef6d8e726168eabbc1c0597d8c4dfdc5fff