Add testrsa.pem from the OpenSSL repo

Found in test/testrsa.pem. Has been around since the SSLeay fork.

testrsa-encrypted.pem was encrypted with AES128 using OpenSSL
1.0.1e-3ubuntu1.1 under the password `password`.

The command used was:

openssl rsa -in testrsa.pem -out testrsa-encrypted.pem -aes128
Add GnuTLS OpenSSL compatibility test keys

key1.pem is encrypted with the password `123456`

key2.pem is encrypted with the password `a123456`

From commit GnuTLS commit f16ef39ef0303b02d7fa590a37820440c466ce8d
Add OpenSSL PEM vector docs
Link to the specific sources of these vectors
Load OpenSSL "traditional" format private keys