Add sp_cert_multi to facilitate SP cert/key rotation #211

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)	53s
Unit test (ubuntu-20.04, 2.4.6)	52s
Unit test (ubuntu-20.04, 2.5.8)	27s
Unit test (ubuntu-20.04, 2.6.6)	34s
Unit test (ubuntu-20.04, 2.7.2)	28s
Unit test (ubuntu-20.04, 3.0.1)	17s
Unit test (ubuntu-20.04, 3.1)	17s
Unit test (ubuntu-20.04, 3.2)	23s
Unit test (ubuntu-20.04, jruby-9.1.17.0)	56s
Unit test (ubuntu-20.04, jruby-9.2.17.0)	1m 2s
Unit test (ubuntu-20.04, jruby-9.3.2.0)	48s
Unit test (ubuntu-20.04, jruby-9.4.0.0)	44s
Unit test (ubuntu-20.04, truffleruby)	1m 54s
Unit test (macos-latest, 2.1.9)	2m 13s
Unit test (macos-latest, 2.2.10)	3m 29s
Unit test (macos-latest, 2.3.8)	2m 11s
Unit test (macos-latest, 2.4.6)	2m 6s
Unit test (macos-latest, 2.5.8)	1m 14s
Unit test (macos-latest, 2.6.6)	59s
Unit test (macos-latest, 2.7.2)	1m 24s
Unit test (macos-latest, 3.0.1)	1m 11s
Unit test (macos-latest, 3.1)	29s
Unit test (macos-latest, 3.2)	39s
Unit test (macos-latest, jruby-9.1.17.0)	1m 16s
Unit test (macos-latest, jruby-9.2.17.0)	59s
Unit test (macos-latest, jruby-9.3.2.0)	1m 13s
Unit test (macos-latest, jruby-9.4.0.0)	1m 5s
Unit test (macos-latest, truffleruby)	5m 4s
finish	0s
	36m 50s

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