Bug in Juju Deployment with conjure up for GCP

We were deploying kuberentes on Google could platform using conjure up. During deployment, we ran into the following problem using the gcp-integrator and kubernetes master :

unit it-gcp-integrator-0: 10:07:27 INFO unit.gcp-integrator/0.juju-log Labelling instance juju-5c0559-9 in europe-west1-b with: {'juju.io/az': 'europe-west1-b', 'juju.io/cloud': 'gce', 'k8s-io-cluster-name': 'kubernetes-t1rxbmojkn8tkr3vouaig2hocl8nn53p'}
unit-gcp-integrator-0: 10:07:29 ERROR unit.gcp-integrator/0.juju-log Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-gcp-integrator-0/charm/reactive/gcp.py", line 68, in handle_requests
    request.instance_labels)
  File "lib/charms/layer/gcp.py", line 125, in label_instance
    '--labels', ','.join('='.join([k, v]) for k, v in labels.items()))
  File "lib/charms/layer/gcp.py", line 253, in _gcloud
    raise GCPError(stderr)
charms.layer.gcp.GCPError: ERROR: (gcloud.compute.instances.add-labels) HTTPError 400: Invalid value for field 'labels': ''. Label key 'juju.io/az' violates format constraints. The key must start with a lowercase character, can only contain lowercase letters, numeric characters, underscores and dashes. The key can be at most 63 characters long. International characters are allowed.

I am more than willing to help fix it, I would like some help so that I do not need to go blindly into the whole repository of juju/conjure-up

It looks like this is where the code is running:
https://github.com/juju-solutions/charm-gcp-integrator/blob/master/reactive/gcp.py#L68

This is part of the GCP integrator charm:

Hi @andrewvd, thanks for reporting this.

I think this is the offending commit: https://github.com/charmed-kubernetes/charm-kubernetes-worker/commit/cb3d6a53c8e932b8a583587ea8abf3c6bee21a63

Regardless of who fixes this, would you mind filing a bug at Bugs : Charmed Kubernetes so we can track it? You can just copy-paste what you described here. Thanks!

cc @cory_fu