Pushed global config to Environment class

Now all stages and hosts can be accessed from the Environment class.
Also made an SSH object part of each host, so commands can be called
each host using the same SSH object, without having to pass the object
around.  This also DRYs up the output handling for ssh and scp commands.

Renamed Action#act to #perform and Part#act to #play to be able to more
easily tell what was getting called.
Use #define_method instead of #method_missing

Also, use Environment info instead of a passed in ssh.