Azure: Support Multiple Service Principals

[Skisocks]

Currently, multiple service principals on container registry resources aren't supported as docker-credential-acr-env cannot identify which principal it should use.

This can be fixed by setting the AZURE_CLIENT_ID env var as the client id of the cluster nodes resource group.

Todo:

• Update the usages of docker-credential-acr-env to support AZURE_CLIENT_ID
• Add the client id to jx-requirements
• Populate client id in jx-requirements in terraform-jx-azure
• Add AZURE_CLIENT_ID to jx gitops variables