[11u] RFR: 8217429: WebSocket over authenticating proxy fails to send Upgrade headers

[Lindenmaier, Goetz]

Hi

I downport this for 11.0.10-Oracle parity.  
http://cr.openjdk.java.net/~goetz/wr20/8217429-websocket_headers-jdk11/01/

I had to add include of HttpRequestImpl in Utils.java to make it compile. 
http://cr.openjdk.java.net/~goetz/wr20/8217429-websocket_headers-jdk11/01/src/java.net.http/share/classes/jdk/internal/net/http/common/Utils.java.udiff.html

Please review.

Original change:
https://bugs.openjdk.java.net/browse/JDK-8217429
http://hg.openjdk.java.net/jdk/jdk/rev/41fa3e6f2785

Best regards,
  Goetz