Add option to do terraform init without initializing backend

[mimadrone]

I see this was raised before, as issue #318, but as it's a thing I would very much like to have, I've gone ahead and written the patch. This is simply an additional field for the Options structure that allows for passing "-backend=false" for terraform init.

[morremeyer]

@yorinasub17 Could you retrigger the tests if the failure is a flake or check what needs to be done?

I'd very much like to have this feature so that we can stop using terraform.RunTerraformCommandE everywhere.

If there's anything else that can be done to help out, please let me know.

Edit: I need to correct myself here, with the setup we use (terraform cloud remote backend), we need to generate an override file anyways as we want to override the whole backend config for all commands. The goal here is to use the local backend with terratest, but the remote backend in the configuration (for actual production use).

[iambalabharathi]

You need any help on this? @mimadrone we need this as soon as possible. What we are doing now to workaround this issue. is bit ugly. :(