Add support for ek certificate chain (stored in TPM NVRAM), resolves #1552

[ematery]

See enhancement-1552: EK Certificate Chain support

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 14 lines in your changes missing coverage. Please review.

Project coverage is 62.58%. Comparing base (d68aa16) to head (1f0fe3e).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
keylime/src/tpm.rs	86.20%	12 Missing ⚠️
keylime-agent/src/main.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

Flag	Coverage Δ
e2e-testsuite	62.58% <84.61%> (+0.33%)	⬆️
upstream-unit-tests	62.58% <84.61%> (+0.33%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
keylime/src/registrar_client.rs	94.01% <100.00%> (ø)
keylime-agent/src/main.rs	17.90% <0.00%> (ø)
keylime/src/tpm.rs	73.61% <86.20%> (+0.87%)	⬆️

... and 6 files with indirect coverage changes

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