Improve coverage of TestLoadPrivateKeyAndSign()
Improve coverage of TestLoadPrivateKeyAndSign()

Martin2112/trillian,gdbelvin/trillian,gtank/trillian,codingllama/trillian,daviddrysdale/trillian,gdbelvin/trillian,google/trillian,codingllama/trillian,RJPercival/trillian,daviddrysdale/trillian,Martin2112/trillian,Martin2112/trillian,google/trillian,RJPercival/trillian,gtank/trillian,AlCutter/trillian,daviddrysdale/trillian,AlCutter/trillian,gdbelvin/trillian