For now this functionality is located in ssl. And existing
public_key function is extended. However some of the functionality may
be moved to public_key in a later stage.

Since no test suites includede test_server.hrl, there is no need
to have test_server in the include path or code path.

This commit adds tests for SNI server support in:
 * ssl_sni_SUITE.erl
 * ssl_to_openssl_SUITE.erl
And some more modifications:
 * make_certs also makes two certs for SNI, and adds
extra options for SNI.

This commit adds support for RFC7301, application-layer protocol
negotiation. ALPN is the standard based approach to the NPN
extension, and is required for HTTP/2.

ALPN lives side by side with NPN and provides an equivalent
feature but in this case it is the server that decides what
protocol to use, not the client.

When both ALPN and NPN are sent by a client, and the server is
configured with both ALPN and NPN options, ALPN will always
take precedence. This behavior can also be found in the OpenSSL
implementation of ALPN.

ALPN and NPN share the ssl:negotiated_protocol/1 function for
retrieving the negotiated protocol. The previously existing
function ssl:negotiated_next_protocol/1 still exists, but has
been deprecated and removed from the documentation.

The tests against OpenSSL require OpenSSL version 1.0.2+.