RFR: JDK-8059000 hgforest: pass options to serve command

[Magnus Ihse Bursie]

Pass options to serve command in hgforest.sh. Mostly necessary for 
--port option.

Original patch was written by Michael Duigou, but it has bit-rotted 
since created so I had to adapt it to the current hgforest.sh.

Bug: https://bugs.openjdk.java.net/browse/JDK-8059000
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8059000-pass-options-to-hgforest-serve/webrev.01

/Magnus