Numa object string representations patch

[Jonte Watford]

The nova scheduler includes a number of very complicated filters with
non-obvious failure modes (the NUMATopologyFilter in particular comes to mind).
It is possible to have a situation where a given instances fails to schedule,
and it is not immediately apparent as to what exactly caused the failure.
Accordingly, it is proposed that we allow for optional detailed messages about
precisely *why* a scheduler filter is failing.

Currently if we are logging at "info" level there is very little
information emitted if a scheduler operation fails. By comparison,
logging at "debug" level generates a large amount of logs, and most
of them aren't important.

If the nova scheduler fails to find a suitable compute node for an instance, it is sometimes tricky to figure out what the problem was. For simple filters (CPU/RAM/disk) the checks are fairly straightforward, but for more complicated filters (PCI, IO ops, and especially NUMA-related things like CPU pinning, huge pages, and hyperthreading) its difficult to manually determine why things failed from looking at the logs. Even with debug logging enabled, there are scenarios where the NUMATopologyFilter filter can fail with no useful logs.

Partially implements blueprint improve-sched-logging

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/600269

[OpenStack Infra (hudson-openstack)]

Change abandoned by Balazs Gibizer (<email address hidden>) on branch: master
Review: https://review.opendev.org/600269
Reason: This patch is old with negative review comments. I'm abandoning it but feel free to restore it or ping me (gibi) on IRC to restore it for you if you want to continue working on it.