Investigate flaky manifest spec

This is a follow-up to fix the manifest import spec related to a broken master incident.

gitlab-org/quality/engineering-productivity/master-broken-incidents#22403 (closed)

The actual failure here was:

     1.1) Failure/Error: expect(page).to have_content 'Complete'
            expected to find text "Complete" in "https://android-review.googlesource.com/platform/build/blueprint group2/build/blueprint Failed Import"

Examination of the spec indicates that we may be relying on connections to external repositories for the spec to pass. This could flake for any number of reasons, but without extra logging here, it's hard to know exactly why the project failed to import. It would be useful to:

• Either avoid external connection, or ensure connection is to a system we control.
• Update the assertion to include import failure reason if desired text is not found.