add support for 'nofail' fstab option. if present, finit's fsck invocation ignores errors for this device.
this is useful if you have an fstab entry for a device with UUID= or LABEL= which isn't always present and which you'd like to not
bail on (so you set nofail). in this case finit leaves the presence-or-not decision to fsck, which exits nonzero.
for block devices that are directly listed in fstab this change isn't important, because for such finit looks for the blockdev's existence and skips the fsck if n/a.
