Add --root-dir option and pass through to magerun

[bobbyshaw]

No description provided.

[bobbyshaw]

This isn't so trivial for the put command as now we don't use a magerun command but use some of the classes for getting DB details. This doesn't allow us to pass --root-dir in.

As we won't be able to do it for the put command, there's no point implementing for the get command. Avoids confusion.

This can be something we look at after removing magerun and implementing our own application root checks and database config reading. See #10.