Code review comment for ~alextu/pc-enablement/+git/oem-scripts:fix-ubr-debsum

`systemctl is-active ubiquity` can be used to check the 1st login well:

verified on this testing:
http://10.102.135.50:8080/job/sanity-3-testflinger-dummy-98000-40004-staging-testing/3/consoleFull

Self-approved:
 - changes beside a75ce41 has been reviewed by Jeremy
 - a75ce41 is discussed with Jeremy and verified passed.
 - So, I merge it directly to save time.