Fix 0.2.9 failures in chutney CI

In legacy/trac#29761 (moved), we discovered that 0.2.9 often fails, and when one allow failures run fails, the next fails too.

I want to add a sleep between allow failures rounds to hopefully allow 0.2.9 to recover.

Should we only add the sleep for 0.2.9? Probably, otherwise we won't notice regressions.

We might also need to:

• adjust the 0.2.9 bootstrap timings
• remove 0.2.9 from CI