mount - Generate correct argv[0] for crunches

* The crunchgen consolidated binary uses argv[0] to determine which program
  to actually run.  The 'mount' program was putting the vfstype in argv[0]
  instead of "mount_<vfstype>".

* This caused crunchgen to run 'hammer' instead of 'mount_hammer'.

* Fixes installer encrypted installs with hammer roots.
loader - unset correct kenv for 'r'ecovery ramdisk mode

* We have to unset vfs.root.real_root instead of lunset vfs.real_root.

* This will properly drop the loader into the recovery ramdisk without
  trying to do any crypt setup or access the root disk in any way (other
  than what it needs to get /boot stuff).
mkinitrd(8): gzip newly produced images

The space savings can be considerable with the current 15MB ramdisk images
beeing reduced to 3.9MB once compressed.