improvement(GCE create_instance): Create GCE lables for instances
improvement(GCE create_instance): Create GCE lables for instances

Creating the tags we have in AWS also as labels in GCE.
Till now we created them only as metadata for instances, but this
information can't be use in other places like billing.

The reason we did not create them as labels is that the label format
is very restricting, allowing only lower case, numbers, dash and
underscore. Hence, the labels aren't going to replace the metadata
and are going to be opportunistic. It means that only if the values
match the format, the labels will be created. Otherwise there is a
warning but the test continues.

scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests