Add option for skipping the gcloud CLI download

[MajorBreakfast]

Adds ability to skip the downloading of the gcloud CLI. Exposing this functionality is important to us because:

• the download functionality adds a lot of unnecessary overhead when running in our ci pipeline which runs in a container image with gcloud pre-installed
• the resources it adds to the terraform plan make the plan harder to read
• it seems to scale not so well with the amount of projects because the gcloud cli is installed once for every module instance instead of once overall

Similar to #369. However, that PR semms to contain other unreleated changes

[MajorBreakfast]

CI failed, but I don't have the permissions to see what went wront

[bharathkkb]

@MajorBreakfast looks like it failed the linting step due to document generation. please run make docker_generate_docs and to test the lint step locally make docker_test_lint.

[MajorBreakfast]

All green now. @bharathkkb Thanks for the instructions!

[morgante]

Thanks for handling this!

[thesuperzapper]

@MajorBreakfast, even with this change, I am still getting my changes polluted like #391.

If we are assuming gcloud will be in the PATH, cant we remove gcloud_bin_abs_path from the triggers of null_resource.run_command?

[MajorBreakfast]

@thesuperzapper The usage of terraform-google-gcloud seems to create two problems. I've created an issue that summarizes them both here #396

[adrian-gierakowski]

@MajorBreakfast is this just a placeholder for something that will be implemented in the future? terraform still seems to try to download gcloud even with skip_gcloud_download = true

looks like it's actually getting stuck when downloading https://github.com/terraform-google-modules/terraform-google-gcloud which is massive due to binaries included in the repo (as mentioned here: terraform-google-modules/terraform-google-gcloud#37