Delay all syncing until the device is provisioned

BUG: 20185340
Add ContentObserver to be notified when device provisioned
system setting bit is flipped. Stash all messages that come
along before then, similar to how we were doing it for
onBootCompleted, and fire them off when ready.

Change-Id: Ied9fe2262b2a96ea3316b6dd7c57e23628e19581