Add explicit and persistent user provisioning state.

Add explicit modelling of provisioning state so that integration
of management provisioning flows with packages such as setup-wizard
are cleaner, and can be more direct. Previously we relied upon
USER_SETUP_COMPLETE secure setting and HOME intents to signal intent,
but this is not very clear and can be fragile.

Bug: 25858670
Change-Id: Idc56a040f710c3aee281db420f21717da3960722