Make BlockDeviceState implement a dict
Make BlockDeviceState implement a dict

While plugins treat the state as just a dictionary, it's nice for the
driver functions to keep state related functions encapsulated in the
state object singleton.  Wrap the internal state dictionary so we can
pass the BlockDeviceState directly without dereferencing.

Change-Id: Ic0193c64d645ed1312f898cbfef87841f460799c

switch-ch/diskimage-builder,switch-ch/diskimage-builder,openstack/diskimage-builder,openstack/diskimage-builder