add support to verify cert chains longer than 1

[gh4683]

Recently found a case where the IAK has both leaf and intermediate certs, and the ca only has the root cert, which was leading to cert verification failure. Fixed it by parsing all certs in the chain and adding the intermediates to the cert pool.

[coveralls]

Pull Request Test Coverage Report for Build 21533221643

Details

• 37 of 41 (90.24%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 53.208%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
service/biz/tpm_cert_verifier.go	37	41	90.24%

Totals
Change from base Build 21499547841:	0.2%
Covered Lines:	2032
Relevant Lines:	3819

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💛 - Coveralls