fix(k8s-gke): specify major K8S version for GKE cluster creation
fix(k8s-gke): specify major K8S version for GKE cluster creation

Right now we use specific K8S version on GKE which are build specific.
Example, currently used one: '1.19.9-gke.1400'
This one became obsolete and not available anymore for usage.
So, instead of providing one another specific version, use 'major'
one to forget such problem as regular sudden GKE cluster creation
failures caused by non-supported versions.

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