Add Env and SetEnv methods to command.Meta to retrieve the current
environment name inside any command.
Make sure all calls to Backend.State contain an environment name, and
make the package compile against the update backend package.
I made this interface way back with the original backend work and I
guess I forgot to hook it up! This is becoming an issue as I'm working
on our 2nd enhanced backend that requires this information and I
realized it was hardcoded before.
This propertly uses the CLIInit interface allowing any backend to gain
access to this data.
During backend initialization, especially during a migration, there is a
chance that an existing state could be overwritten.
Attempt to get a locks when writing the new state. It would be nice to
always have a lock when reading the states, but the recursive structure
of the Meta.Backend config functions makes that quite complex.
