Bug: Key creation failure if byte 27 of key data is 0x30

[djones6]

If you try to create an RSA key with data where byte 27 happens to be 0x30, key creation fails.

I tracked this down to an unsafe assumption in the stripX509CertificateHeader function:
https://github.com/IBM-Swift/BlueRSA/blob/master/Sources/CryptorRSA/CryptorRSAUtilities.swift#L228
which is called here:
https://github.com/IBM-Swift/BlueRSA/blob/master/Sources/CryptorRSA/CryptorRSAKey.swift#L624

I found this while debugging intermittent test failures in the CI. The symptom on Linux is a crash because we don't handle a failure from OpenSSL properly - I have a fix for that in the issue.swift51 branch, but I haven't figured out what to do about this problem yet.