fix(gce-sct-runner): keep instance alive
fix(gce-sct-runner): keep instance alive

Since Cloud instance stopper supports only tags/labels
we need to set the instance keep tag to alive.
This is needed to prevent Cloud instance stopper script
to kill the SCT Runner

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