GPII-3940: Upgrade terrafrom and providers

[stepanstipl]

This PR:

• updates Terraform
• updates Google Cloud SDK
• updates kubectl
• updates Helm
• updates Terragrunt
• updates all Terraform providers to the latest
• moves to vanilla Helm provider, as the changes we needed have been merged upstream

This mainly fixes node_pool recreation due to metadata config - see GoogleCloudPlatform/magic-modules#1507 for details.

Update:
Helm update was reverted due to an issue with spec validation (see helm/helm#5750). This should be fixed in soon to be 0.14.1, but it was not available at the time of this PR yet.

This should be tagged as 0.6.0-google_gpii.0 once merged.

Also:

• I've tried to upgrade to Alpine 3.9, but failed due to issue with compiling grpc with newer gcc version (see WIP: Add a gcc-8.1 portability test for c and make it pass grpc/grpc#15532), ticket has been created to pick this up: GPII-3947
  Upgrade exekube to latest Alpine
• We don't scan exekube image atm, a ticket for that has been created as well - GPII-3946
  Scan exekube docker image for vulnerabilities
• Google provider now prefers to use location field for GKE clusters and node-pools, the old zone and region have been deprecated (see https://www.terraform.io/docs/providers/google/r/container_cluster.html#location). We should abandon the deprecated fields in favor of location, this will also allow us to get rid of the 2 resources split for regional/zonal clusters in gke-cluster module. Ticket created - GPII-3949
  Use location in cluster and node_pool resources in gke-cluster exekube module

Upstream PR has been opened - exekube#124.

[mrtyler]

LGTM

Needs an exekube version bump.

[natarajaya]

LGTM!

Should this be proposed to upstream as well?

[amatas]

LGTM

[stepanstipl]

Thanks for reviews, I've

• bumped the exekube google version to 0.6.0
• opened upstream PR - Upgrade Terraform, providers and other various components exekube/exekube#124
• reverted Helm upgrade after testing (see notes above)
• opened several related tickets (see notes above)