hg: jdk/sandbox: 8231506: Fix some instabilities in a few networking tests

[chris.hegarty at oracle.com]

Changeset: 54de0c861d32
Author:    dfuchs
Date:      2019-10-01 12:10 +0100
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/54de0c861d32

8231506: Fix some instabilities in a few networking tests
Reviewed-by: alanb, chegar, msheppar

! test/jdk/java/net/MulticastSocket/UnreferencedMulticastSockets.java
! test/jdk/java/net/SocketImpl/SocketImplCombinations.java
! test/jdk/java/net/httpclient/DigestEchoServer.java