fix usage and check $PATH
bugfixes + code cleanup

- new functions:
    * bind_chroot()
    * unbind_chroot()
    * wait_for_device()
    * summarize_instance()
- mount /dev/pts in chroot (some programs need this).
- add cleanup function/trap for make_bootable_drive().
- don't umount chroot or delete loopbacks when NOCLEAN is set.
- added variable $base_part for `/dev/mapper/$(basename $base_loop)p1' path.
- wrapped commands and comments at 80 cols (hi mom!!!!).
- move pre_grub() call closer to actual GRUB work, pretty print, etc.
wrap at 80 cols
conditionally enable acpi hotplugging

this allows vnics to work better when attached to guests
invsblduck's plugin examples