RFR: 8055331 : (xs) hgforest.sh cleaner handling of sub-process non-zero exit result

[Mike Duigou]

Hello all;

This changeset breaks out some the simple and non-controversial changes from JDK-8042841. The change makes it easier to write scripts around hg incoming, outgoing, etc. that return exit code 1 for non-error situations. Rather than returning 1 for all non-zero exit conditions hgforest will instead return the highest exit code encountered.

jbsbug: https://bugs.openjdk.java.net/browse/JDK-8055331
webrev: http://cr.openjdk.java.net/~mduigou/JDK-8055331/0/webrev/

Mike