[8u] RFR 8185898: setRequestProperty(key, null) results in HTTP header without colon in request

[Yuri Nesterenko]

Hi,

please review this request for a backport to 8u.

Original issue:

    https://bugs.openjdk.java.net/browse/JDK-8185898

    https://hg.openjdk.java.net/jdk/jdk/rev/0211b062843d

The patch itself applied good enough; I had to adapt the test for JDK8.

Look for webrev here:

    http://cr.openjdk.java.net/~yan/8185898/webrev.0/

Thank you!

--yan