[google] generate and store cluster name

[drnic]

Bootstrapping new google cluster will now generate a random cluster name prefixed (like now) with your local whoami.

$ bootstrap-kubernetes-demos up --google
...

$ tree state
state
├── configuration
├── google
│   └── cluster-name
├── infrastructure
└── systems
    └── zzz-ignoreme
$ cat state/google/cluster-name
drnic-4hdsyy
$ gcloud container clusters list
NAME          LOCATION    MASTER_VERSION  MASTER_IP      MACHINE_TYPE   NODE_VERSION   NUM_NODES  STATUS
drnic-4hdsyy  us-west1-a  1.14.6-gke.13   35.247.69.161  n1-standard-2  1.14.6-gke.13  3          PROVISIONING

$ bootstrap-kubernetes-demos down
Deleting cluster drnic-4hdsyy...⠏