RFR : 8038435 : Some hgforest.sh commands don't receive parameters

[Mike Duigou]

Hello all;

I introduced bug in JDK-8030681 which prevents non-clone commands from receiving parameters.

I also slightly cleaned up checking for what is an acceptable root repo as I had encountered this in a problem with a local clone and reverted prior change which made the script a bash script. 

bug:    https://bugs.openjdk.java.net/browse/JDK-8038435

webrev: http://cr.openjdk.java.net/~mduigou/JDK-8038435/0/webrev/

Thanks,

Mike