Add sp_cert_multi to facilitate SP cert/key rotation #213

Job	Run time
Unit test (ubuntu-20.04, 2.1.9)	51s
Unit test (ubuntu-20.04, 2.2.10)	57s
Unit test (ubuntu-20.04, 2.3.8)	54s
Unit test (ubuntu-20.04, 2.4.6)	51s
Unit test (ubuntu-20.04, 2.5.8)	25s
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)	15s
Unit test (ubuntu-20.04, 3.1)	16s
Unit test (ubuntu-20.04, 3.2)	14s
Unit test (ubuntu-20.04, jruby-9.1.17.0)	55s
Unit test (ubuntu-20.04, jruby-9.2.17.0)	1m 0s
Unit test (ubuntu-20.04, jruby-9.3.2.0)	42s
Unit test (ubuntu-20.04, jruby-9.4.0.0)	43s
Unit test (ubuntu-20.04, truffleruby)	1m 58s
Unit test (macos-latest, 2.1.9)	1m 57s
Unit test (macos-latest, 2.2.10)	2m 41s
Unit test (macos-latest, 2.3.8)	2m 20s
Unit test (macos-latest, 2.4.6)	2m 11s
Unit test (macos-latest, 2.5.8)	1m 4s
Unit test (macos-latest, 2.6.6)	1m 14s
Unit test (macos-latest, 2.7.2)	1m 9s
Unit test (macos-latest, 3.0.1)	28s
Unit test (macos-latest, 3.1)	34s
Unit test (macos-latest, 3.2)	1m 20s
Unit test (macos-latest, jruby-9.1.17.0)	1m 12s
Unit test (macos-latest, jruby-9.2.17.0)	3m 31s
Unit test (macos-latest, jruby-9.3.2.0)	1m 8s
Unit test (macos-latest, jruby-9.4.0.0)	1m 8s
Unit test (macos-latest, truffleruby)	4m 58s
finish	0s
	37m 48s

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