Add a use_master_when_local option to allow remote execution while using...

... a local file_client

This PR allows for remote execution while using a salt master for remote execution. This option will obviously have some side effects. For instance, the cp module will be slightly confusing, as it will trigger a cp to/from the minion to/from the master, which in this case would also be the minion.

However, this option makes it possible to do salt runs from the master successfully.