Add /sbin and /usr/sbin to the search path
Add /sbin and /usr/sbin to the search path

Some tools (such as dumpe2fs) may reside in paths that are not in the system
non-root path.

BUG=chromium-os:13564
TEST=Can now run sign_official_build without sudo.

Change-Id: I48737e7735551c9004a6fa19359da664ca67b423
Reviewed-on: http://gerrit.chromium.org/gerrit/867
Reviewed-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Tested-by: Gaurav Shah <2987db6a10bcfe664554a372d01e80df7fd325a3@chromium.org>

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