Fetch $ZFS_MOUNTPOINT from the environment instead of assuming
it directly under "/${ZFS_VOLUME}"
Get rid of hardcoded /var/portbuild, which is now /a/portbuild
Fix name of qmanager rc script in comment.
Clean out another instance of /var/portbuild
determine if the build will be a pkgng build or a pkg_install build base on
bsd.port.mk, not on /etc/make.conf, this allows build to autodetermine that on
current the default is pkgng

Tested by:	erwin
Actually use first argument and not scriptname
for figuring out which arch to run on.