Add sp_cert_multi to facilitate SP cert/key rotation #218

Job	Run time
Unit test (ubuntu-20.04, 2.1.9)	52s
Unit test (ubuntu-20.04, 2.2.10)	1m 1s
Unit test (ubuntu-20.04, 2.3.8)	55s
Unit test (ubuntu-20.04, 2.4.6)	53s
Unit test (ubuntu-20.04, 2.5.8)	27s
Unit test (ubuntu-20.04, 2.6.6)	27s
Unit test (ubuntu-20.04, 2.7.2)	25s
Unit test (ubuntu-20.04, 3.0.1)	16s
Unit test (ubuntu-20.04, 3.1)	15s
Unit test (ubuntu-20.04, 3.2)	15s
Unit test (ubuntu-20.04, jruby-9.1.17.0)	55s
Unit test (ubuntu-20.04, jruby-9.2.17.0)	54s
Unit test (ubuntu-20.04, jruby-9.3.2.0)	46s
Unit test (ubuntu-20.04, jruby-9.4.0.0)	46s
Unit test (ubuntu-20.04, truffleruby)	1m 57s
Unit test (macos-latest, 2.1.9)	1m 54s
Unit test (macos-latest, 2.2.10)	5m 25s
Unit test (macos-latest, 2.3.8)	2m 10s
Unit test (macos-latest, 2.4.6)	2m 10s
Unit test (macos-latest, 2.5.8)	1m 2s
Unit test (macos-latest, 2.6.6)	1m 18s
Unit test (macos-latest, 2.7.2)	1m 7s
Unit test (macos-latest, 3.0.1)	30s
Unit test (macos-latest, 3.1)	24s
Unit test (macos-latest, 3.2)	50s
Unit test (macos-latest, jruby-9.1.17.0)	1m 23s
Unit test (macos-latest, jruby-9.2.17.0)	1m 8s
Unit test (macos-latest, jruby-9.3.2.0)	1m 4s
Unit test (macos-latest, jruby-9.4.0.0)	1m 7s
Unit test (macos-latest, truffleruby)	9m 26s
finish	0s
	42m 2s

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