In LP: 2009797, an exception of this form happens:
AttributeError: 'FilesystemController' object has no attribute '_start_task'
The installer client, u-d-i, is asking for storage information ASAP
after the socket starts listening, and in this case that happened before
all controllers were started. The sync primitive the probe is waiting
on wasn't created yet.
With one known exception, /meta/status, we really shouldn't be
responding to random API calls, and the startup sequence of the
controllers should be relatively quick (sub 1 second to be sure).
Just delay them, except for the special one.
22c3987db5