J. David Lowe 8552d8ec20 etcdserver: don't activate alarm w/missing AlarmType
Narrowly prevent etcd from crashing when given a bad ACTIVATE payload, e.g.:

$ curl -d "{\"action\":\"ACTIVATE\"}" ${ETCD}/v3/maintenance/alarm
curl: (52) Empty reply from server
2021-06-04 12:18:56 -07:00
..
2021-06-03 16:07:01 +02:00
2021-06-03 16:07:01 +02:00