Remove the first argument to panic(), which was initially
intended to be the exit code, however when a non-zero exit
code was returned to release/Makefile, this would prevent
any remaining (and possibly successful) stages from being
attempted.

If the vm-base target fails, prevent the vm-image target
from being run since it cannot possibly succeed.

Add /usr/local/bin and /usr/local/sbin to PATH, needed
if third-party software needs to use utilities outside
of the base system during post-install stages (indexinfo
is one culprit).