Add tests for supervisor request handlers #9042

Job	Run time
build / Build	7m 10s
Integration Tests (certrotation)	1m 26s
Integration Tests (cacertrotation)	1m 18s
Integration Tests (etcdrestore)	1m 39s
Integration Tests (localstorage)	1m 18s
Integration Tests (startup)	6m 53s
Integration Tests (custometcdargs)	28s
Integration Tests (etcdsnapshot)	7m 43s
Integration Tests (kubeflags)	6m 32s
Integration Tests (longhorn)	2m 24s
Integration Tests (secretsencryption)	1m 45s
Integration Tests (flannelnone)	1m 2s
	39m 38s

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