Update terraform-fmt to match terraform-validate (gruntwork-io#46)

This PR updates the `terraform-fmt` hook as follows:

1. Run with `-diff -check` so the differences are printed, rather than made on disk.
1. Instead of exiting on the first error, save the exit codes, and print out all `fmt` errors before exiting.

These changes are very similar to gruntwork-io#45.

Merge pull request gruntwork-io#44 from parkalla86/update-shebang-tf-sh

Updated shebang to #!/usr/bin/env bash

Merge pull request gruntwork-io#35 from shmileee/helmlint-serial

Run helmlint hook as single process

Merge pull request gruntwork-io#32 from gruntwork-io/yori-fix-tfvalidate

Fix terraform-validate hook

Merge pull request gruntwork-io#30 from gruntwork-io/pull-request-29

Extend gruntwork-io#29

Merge pull request gruntwork-io#25 from 06kellyjac/shellcheck_optionals

Shellcheck optionals

Merge pull request gruntwork-io#26 from AlainODea/ao-tgenv-support

Support tfenv+tgenv

Merge pull request gruntwork-io#24 from gruntwork-io/yori-check-skipenv

Check skipenv

Merge pull request gruntwork-io#23 from gruntwork-io/yori-terragrunth…

…clfmt

Terragrunt hclfmt hook

Merge pull request gruntwork-io#20 from gruntwork-io/yori-fix-tffmt-bug

Fix terraform fmt hook where it is now running on all files regardless of exclude