When hosts are filtered for a request, and no host passes all the
filters, operators can only see the last filter run; they have no
visibility into which filter removed which host. This attempts to
improve this situation by tracking the hosts remaining after each
filter is run and the number of hosts removed. If no host is left, to
log that information along with the reservation ID and instance UUID
of the request. Since that can be a lot of information, it will call
LOG.info with just the counts for all but the final filter, which
will contain the last deleted host names; LOG.debug will output the
full record of each filter and the hosts remaining after each step.
This will better enable operators to determine why a particular host
was not selected.
Change-Id: I6173274a03bd8712eb4d63c7a998bb02abdecf4b
Blueprint: no-valid-host-reporting
0f67836de2