* Updates to concurrent series upgrade
Updates to make it run more in parallel and spend less time waiting on
the whole model when updating machines.
* Make the concurrent series upgrade tests work
This is a number of changes to get the concurrent (here called
'parallel' historically) series upgrade tests to work. A number of
changes were required which included limiting the number of concurrent
async co-routines (futures) that could be run as with large models it
hits the limits of the Py3 runtime.
* Fix the tests and change pause order in maybe_pause_things
Due to an additional model helper call, an additional model AsyncMock is
required. Also the pause order had changed, and this is restored to
ensure the original design is retained (for pause order).
Clean up some commented out code and sort out a few PEP8 errors.
* Update comment to reflect code (3 -> 4)
* Fix tests that fail on bionic but pass on focal
Essentially, asyncio.gather has different behaviour on bionic that
focal. Although this doesn't affect testing, it does affect the unit
tests. These changes are simply to normalise the behaviour of unit
tests on focal and bionic.
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