Change Terraform commands to use -chdir to avoid having to cd

[nick-stroud]

Output now looks like:

Terraform group was successfully created in directory hpc-cluster-small/primary
To deploy, run the following commands:
  terraform -chdir=hpc-cluster-small/primary init
  terraform -chdir=hpc-cluster-small/primary apply

Tested: manually ran ghpc create with multi group yaml and deployed both resource groups with outputted commands.

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