tpm: check if EK certificate has valid ASN.1 DER encoding

[THS-on]

Further this removes padding found on some TPMs in the NV indices.
If this is not valid, we still use it, but output a warning.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.92%. Comparing base (2f7b3ad) to head (c92b617).
Report is 52 commits behind head on master.

Files with missing lines	Patch %	Lines
keylime/src/tpm.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

Flag	Coverage Δ
e2e-testsuite	61.92% <77.77%> (+4.33%)	⬆️
upstream-unit-tests	61.92% <77.77%> (+10.91%)	⬆️

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

Files with missing lines	Coverage Δ
keylime/src/tpm.rs	71.55% <77.77%> (+5.37%)	⬆️

... and 9 files with indirect coverage changes