Proxy Issues in ConnectorProviders

Since the built-in Client uses `HttpURLConnection` and can only use a proxy if it is globally via system properties, I've looked into the other offered connector providers and stumbled onto some issues.

See SSCCE for this issue https://github.com/leonard84/jersey-issues-3655

* JDK Connector seems to expect SSL even if a plain http is made, or something else
* Netty has the same problem
* Netty and JDK use `CONNECT` even for http so there might be the cause
* NettyConnector calls `io.netty.handler.proxy.HttpProxyHandler#HttpProxyHandler(java.net.SocketAddress, java.lang.String, java.lang.String)` even if only `ClientProperties.PROXY_URI` is set, causing a NPE, it should check for null and call `io.netty.handler.proxy.HttpProxyHandler#HttpProxyHandler(java.net.SocketAddress)` instead.
* Connectors have different error handling if Proxy returns 403:
* Apache will return a response with 403
* Jdk fails with `java.io.IOException: "Connecting to proxy failed with status 403."`
* Grizzly and Jetty work for HTTP and return a response with 403
* Jetty fails for HTTPS with `javax.ws.rs.ProcessingException: java.util.concurrent.ExecutionException: org.eclipse.jetty.client.HttpResponseException: Unexpected HttpResponse[HTTP/1.1 403 Forbidden]@3e3692a6 for HttpRequest[CONNECT localhost:1337 HTTP/1.1]@fdb79f3
`
* GrizzlyConnector fails when the Proxy returns 403 when using `CONNECT` for HTTPS and blocks indefinetly.
```
java.lang.NullPointerException: null
at org.glassfish.grizzly.http.HttpClientFilter$ClientHttpResponseImpl.getProcessingState(HttpClientFilter.java:714) ~[grizzly-http-2.4.0.jar:2.4.0]
at com.ning.http.client.providers.grizzly.HttpTransactionContext.currentTransaction(HttpTransactionContext.java:134) ~[grizzly-http-client-1.13.jar:na]
at com.ning.http.client.providers.grizzly.AhcEventFilter.onHttpHeaderError(AhcEventFilter.java:261) ~[grizzly-http-client-1.13.jar:na]
at org.glassfish.grizzly.http.HttpCodecFilter.handleRead(HttpCodecFilter.java:627) ~[grizzly-http-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.http.HttpClientFilter.handleRead(HttpClientFilter.java:175) ~[grizzly-http-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119) ~[grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:539) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56) [grizzly-framework-2.4.0.jar:2.4.0]
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137) [grizzly-framework-2.4.0.jar:2.4.0]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_141]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_141]
```

Start with the linked SSCCE repository and reproduce the proxy cases for plain HTTP, HTTPS CONNECT, missing proxy credentials, and proxy status 403. Trace the JDK, Netty, Grizzly, Jetty, and Apache connector-provider paths to compare their behavior. Done means the reported SSL, null-pointer, response-handling, and indefinite-blocking failures have defined and consistent outcomes.

Written by the indexing model from the issue text.