Add further tests for new RSA keys
Add further tests for new RSA keys

For uniformity, this commit adds tests for DER encoded, SHA1-2DES and SHA1-RC4-128-encrypted RSA keys; for SHA1-3DES encrypted keys, these were already present.

ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls