Add sp_cert_multi to facilitate SP cert/key rotation #206

Job	Run time
Unit test (ubuntu-20.04, 2.1.9)	44s
Unit test (ubuntu-20.04, 2.2.10)	52s
Unit test (ubuntu-20.04, 2.3.8)	52s
Unit test (ubuntu-20.04, 2.4.6)	48s
Unit test (ubuntu-20.04, 2.5.8)	26s
Unit test (ubuntu-20.04, 2.6.6)	26s
Unit test (ubuntu-20.04, 2.7.2)	26s
Unit test (ubuntu-20.04, 3.0.1)	16s
Unit test (ubuntu-20.04, 3.1)	18s
Unit test (ubuntu-20.04, 3.2)	15s
Unit test (ubuntu-20.04, jruby-9.1.17.0)	38s
Unit test (ubuntu-20.04, jruby-9.2.17.0)	55s
Unit test (ubuntu-20.04, jruby-9.3.2.0)	44s
Unit test (ubuntu-20.04, jruby-9.4.0.0)	41s
Unit test (ubuntu-20.04, truffleruby)	1m 53s
Unit test (macos-latest, 2.1.9)	1m 36s
Unit test (macos-latest, 2.2.10)	2m 49s
Unit test (macos-latest, 2.3.8)	1m 58s
Unit test (macos-latest, 2.4.6)	2m 1s
Unit test (macos-latest, 2.5.8)	57s
Unit test (macos-latest, 2.6.6)	59s
Unit test (macos-latest, 2.7.2)	3m 11s
Unit test (macos-latest, 3.0.1)	29s
Unit test (macos-latest, 3.1)	29s
Unit test (macos-latest, 3.2)	30s
Unit test (macos-latest, jruby-9.1.17.0)	3m 21s
Unit test (macos-latest, jruby-9.2.17.0)	1m 10s
Unit test (macos-latest, jruby-9.3.2.0)	2m 20s
Unit test (macos-latest, jruby-9.4.0.0)	1m 3s
Unit test (macos-latest, truffleruby)	4m 49s
finish	0s
	37m 56s

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