cashew: don't propagate inactive plans to clients

Filter inactive (future, expired, consumed) plans when responding to
client D-Bus requests or emitting D-Bus signals.

BUG=chromium-os:9397
TEST=unit tests, manual testing on device

Change-Id: Ie221823627b3864802100aa619aa04b8cb949ac7

Review URL: http://codereview.chromium.org/5321001