Force powershell on local-exec

[yorinasub17]

Depends on gruntwork-io/kubergrunt#74

If you look at the code for local-exec, it turns out that it hard codes to cmd instead of doing something intelligent to see if it is run from powershell or cmd. See https://github.com/hashicorp/terraform/blob/master/builtin/provisioners/local-exec/resource_provisioner.go#L79

Unfortunately, cmd doesn't quite cleanly support multiline commands when passed using the /C arg, so instead we need to force Powershell when on windows by using the interpreter attribute.

Additionally, environment variables are read as $env:ENV_VAR on Powershell, so we need to adapt to that as well.

I also ran into issues with json encoding, where the double quotes made Powershell unhappy, so we need to escape those as well.

Testing note

• Test on windows box

[yorinasub17]

Ok I have verified the current version works on my windows box.

[yorinasub17]

Ah looks like there is still a problem with windows. Specifically, the kubectl auth system doesn't work. Since we've run into a few issues with kubectl anyway, I'll work on creating a wrapper in kubergrunt that can run arbitrary kubectl auth'd (since I have verified kubergrunt is properly authing).

[robmorgan]

LGTM

[yorinasub17]

Thanks for the review! Going to merge this now that kubergrunt is merged.