Add sp_cert_multi to facilitate SP cert/key rotation #225

Job	Run time
Unit test (ubuntu-20.04, 2.1.9)	47s
Unit test (ubuntu-20.04, 2.2.10)	56s
Unit test (ubuntu-20.04, 2.3.8)	59s
Unit test (ubuntu-20.04, 2.4.6)	55s
Unit test (ubuntu-20.04, 2.5.8)	28s
Unit test (ubuntu-20.04, 2.6.6)	37s
Unit test (ubuntu-20.04, 2.7.2)	29s
Unit test (ubuntu-20.04, 3.0.1)	15s
Unit test (ubuntu-20.04, 3.1)	16s
Unit test (ubuntu-20.04, 3.2)	17s
Unit test (ubuntu-20.04, jruby-9.1.17.0)	54s
Unit test (ubuntu-20.04, jruby-9.2.17.0)	54s
Unit test (ubuntu-20.04, jruby-9.3.2.0)	51s
Unit test (ubuntu-20.04, jruby-9.4.0.0)	46s
Unit test (ubuntu-20.04, truffleruby)	1m 58s
Unit test (macos-latest, 2.1.9)	1m 52s
Unit test (macos-latest, 2.2.10)	2m 10s
Unit test (macos-latest, 2.3.8)	2m 6s
Unit test (macos-latest, 2.4.6)	2m 8s
Unit test (macos-latest, 2.5.8)	57s
Unit test (macos-latest, 2.6.6)	1m 34s
Unit test (macos-latest, 2.7.2)	1m 25s
Unit test (macos-latest, 3.0.1)	34s
Unit test (macos-latest, 3.1)	33s
Unit test (macos-latest, 3.2)	28s
Unit test (macos-latest, jruby-9.1.17.0)	1m 14s
Unit test (macos-latest, jruby-9.2.17.0)	1m 4s
Unit test (macos-latest, jruby-9.3.2.0)	1m 2s
Unit test (macos-latest, jruby-9.4.0.0)	1m 4s
Unit test (macos-latest, truffleruby)	8m 13s
finish	5s
	37m 51s

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