Fix make_dev_ssd.sh --remove_rootfs_verification
Fix make_dev_ssd.sh --remove_rootfs_verification

It was checking for /dev/dm-0, which isn't the case anymore.  It now
always attempts to remove rootfs verification from the command line;
this is harmless (no-op) if it's already removed.

BUG=chromium-os:31558
TEST=manual

/usr/share/vboot/bin/make_dev_ssd.sh --remove_rootfs_verification
reboot
touch /opt/google/chrome/chrome

Change-Id: I62dc138e8d1d09bdcb16be3faab74d32c5f7675a
Signed-off-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28506
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

acorn-marvell/vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,ccaapton/vboot_reference,geekboxzone/mmallow_external_vboot_reference,marineam/seismograph,marineam/seismograph,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,ionave/seismograph,ionave/seismograph,acorn-marvell/vboot_reference,ccaapton/vboot_reference,acorn-marvell/vboot_reference,ionave/seismograph,ccaapton/vboot_reference,marineam/seismograph,marineam/seismograph,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,ccaapton/vboot_reference,coreboot/vboot