OpenSSLKey: easier creation and use of OpenSSL keys

For some future changes, it will be easier to convert OpenSSL objects to
real objects and back from native pointers. Make it easier to add new
EVP_PKEY types without adding them in if/else statements everywhere.

Change-Id: I19095bfc5f00835a266f572bc62e2e8d0a8cd544
17 files changed