If the install media contains non-free /*firmware*.tgz files, use fw_update

If the install media contains non-free /*firmware*.tgz files, use fw_update
to install them.  This lets users usb-lift firmware on a preloaded install70.img
image like this:
    # vnconfig install70.img
    vnd0
    # (mount /dev/vnd0a /mnt && cd /mnt && fw_update -F iwm iwx iwn intel)
    # umount /mnt && vnconfig -u vnd0
The firmwares are installed after the sets, then all network drivers are
re-configured in the hope that new firmwares have showed up.  The install
script continues to attempt a network firmware install, which might pull/update
additional firmwares.
work done with afresh1