Custom backend script

[philpep]

I'd be nice to create custom backend just by giving a path to a script that will actually run commands.

testinfra -c script:///path/to/mybackend --hosts hostspec

This would provide a way to implement lxd/lxc, $CLOUD_SOFTWARE, $NEW_CONTAINER_SOFTWARE without modifying testinfra.

[UtahDave]

@philpep I just made an lxc backend based off the docker backend. Would you be interested in a PR with the lxc backend or would you rather just have a generic backend like you describe above?

[UtahDave]

Hm. Just found https://github.com/philpep/testinfra/pull/134

[dAnjou]

I think I like the approach in #10 better.