Allow inclusion of client certificate while not verifying server certificate

The connection_adapter was setting SSL_VERIFY_PEER when :pem or :pk12 options were specified; but, it's possible that I want to disable server certificate validation (:verify => false) while at the same time providing a client certificate.  This pull request allows for the :verify option to still work even if a PEM or PK12 client certificate are specified.

From what I saw here (https://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html#NOTES) it looks like the setting is independent for client and server, so the simple presence of a client cert should not require me to verify a server certificate.