Allow factory install shim run without uuidgen

Since there are some boards does not have uuidgen, the script is
modified so that uuidgen become optional.

BUG=chrome-os-partner:21700
TEST=None

Change-Id: If7b17ca581f09f4f6524aec8b89e007e973baa1b
Reviewed-on: https://gerrit.chromium.org/gerrit/64764
Commit-Queue: Chun-Yen Ho <[email protected]>
Tested-by: Chun-Yen Ho <[email protected]>
Reviewed-by: Hung-Te Lin <[email protected]>
1 file changed