Update to the latest 2013.09.01 ISO
Wait a bit longer for the network to settle
Add a workaround for the shutdown race condition

http://comments.gmane.org/gmane.linux.arch.general/48739

Basically systemd kills the networking before it kills ssh sessions, and
Packer will try and wait for a 0 exit code after the shutdown command to
confirm that it worked. Things happen too quickly with systemd, and so
Packer complains when gracefully halting the machine that:

    "Build 'vmware' errored: Shutdown command has non-zero exit status."

This workaround just adds a standard systemd timer to the poweroff
command so it has a one second delay, which is long enough for the
0 exit code to return and signal a successful graceful halt.