OpenSslEngine skip ALPN tests if OpenSsl version doesn't support ALPN

Motivation:
OpenSslEngine now tests ALPN behavior. However it is possible that OpenSSL is present, but the version does not support ALPN. This will result in test failures instead of just skipping the test.

Modifications:
- Skip ALPN tests in OpenSslEngineTest if the version of OpenSSL does not support ALPN

Result:
Tests don't fail due to unsupported feature in OpenSSL.

Author: Scottmitch

handler/src/test/java/io/netty/handler/ssl/OpenSslEngineTest.java

@@ -40,6 +40,7 @@ public void testNpn() throws Exception {
     @Test
     public void testAlpn() throws Exception {
         assumeTrue(OpenSsl.isAvailable());
+        assumeTrue(OpenSsl.isAlpnSupported());
         ApplicationProtocolConfig apn = acceptingNegotiator(Protocol.ALPN,
                 PREFERRED_APPLICATION_LEVEL_PROTOCOL);
         setupHandlers(apn);
@@ -49,6 +50,7 @@ public void testAlpn() throws Exception {
     @Test
     public void testAlpnCompatibleProtocolsDifferentClientOrder() throws Exception {
         assumeTrue(OpenSsl.isAvailable());
+        assumeTrue(OpenSsl.isAlpnSupported());
         ApplicationProtocolConfig clientApn = acceptingNegotiator(Protocol.ALPN,
                 FALLBACK_APPLICATION_LEVEL_PROTOCOL, PREFERRED_APPLICATION_LEVEL_PROTOCOL);
         ApplicationProtocolConfig serverApn = acceptingNegotiator(Protocol.ALPN,