api: Ensure WaitForFrontend blocks
Created by: tsenart
This renames RetryPingUntilAvailable
to WaitForFrontend
which
replaces the previous package level functions of the same name.
That function was previously assumed to be blocking until the frontend was available, but it instead timed out after 5 seconds.
We were seeing problems in development where repo-updater failed because migrations hadn't been ran yet. This meant that we weren't waiting for the frontend until it was actually ready.
This commit changes that.
Part of #2025 (closed)