Add support for passing through flags

[msmuenchen]

Particularly in large Terraform installations (such as if you manage large, multi-thousand-records sized DNS zones), a plain tftarget apply can take many minutes to load.

It would be very appreciated if one could pass through arbitrary flags (e.g. -refresh=false or, per #11, -target) to Terraform to reduce the amount of time needed to run.

[pataquets]

@msmuenchen I've just seen #28, which might solve your issue. Not tested myself, not sure if documented, just seen the linked issue and thought it might help you. Let us know if it does.