Use a second level of subparsers in the CLI #1007

Job	Run time
build	7m 5s
build-ceph	1m 54s
pytest (cli)	2m 22s
demo	3m 33s
pytest (state)	1m 51s
discovery (container)	3m 56s
pytest (multi_gateway)	2m 11s
discovery (embedded)	3m 32s
ha (sanity)	3m 56s
pytest (server)	2m 23s
ha (state_transitions)	3m 47s
pytest (grpc)	3m 40s
ha (state_transitions_both_gws)	4m 50s
pytest (omap_lock)	5m 3s
ha (state_transitions_loop)	12m 34s
pytest (old_omap)	1m 56s
ha (state_transitions_rand_loop)	20m 31s
pytest (log_files)	3m 38s
pytest (nsid)	3m 2s
push-to-registry	0s
	1h 31m 44s

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