Add async support to the DBus block* & flight_mode

Add asynchronous support to the DBus block* and flight_mode
methods.  This allows urfkill to process responses from
ofono and pass thru failures including InProgress and
EmergencyMode.  This support also leverages the new pre-soft
state recently added to UrfConfig.
UrfKillswitch: get rid of saved_state

The killswitch saved_state attribute is no longer used
by the arbitrator so it can be safely removed now.
UrfDaemon: save persist state for block DBus calls

When a block DBus call succeeds, make sure to save
the persist state of the killswitch.
UrfDeviceHybris: properly initialize object_path