improvement(keep_alive): set to 11 hours
improvement(keep_alive): set to 11 hours

Cloud instance stopper stops GCE instances if
they are 11 hours old and untagged, and for AWS
the value is set to 12 hours. So selecting the min
between those to make sure our instances are not
stopped prematurely.

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