fix(monitoring_download): revert to master dashboard if not available
fix(monitoring_download): revert to master dashboard if not available

when monitoring doesn't have dashboards for the scylla version we
are using, revert to use the master dashboard

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