Comment 10 for bug 1790721

Reviewed: https://review.openstack.org/599875
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=dcd421ae9e6f0391fea06c9d20949267354c3b3c
Submitter: Zuul
Branch: master

commit dcd421ae9e6f0391fea06c9d20949267354c3b3c
Author: Matt Riedemann <email address hidden>
Date: Tue Sep 4 20:57:33 2018 -0400

    Fix nova-status "_check_resource_providers" check

    The way in which this check counted compute nodes was
    broken because of an incorrect for/else condition. If
    the check is run with a nova.conf like we have in
    devstack, where the API database is configured but
    the [database]/connection is pointing at cell0, where
    there are no compute nodes, the check passes saying
    there are no compute nodes even if the are compute
    nodes found in the cell databases (in the for loop).
    This is because the else executes because the for loop
    doesn't break, and then _count_compute_nodes returns 0
    for cell0 and overwrites the num_computes variable.

    This fixes the issue by checking if we have cell mappings
    before running the loop, else we hit the else block as
    was originally intended.

    Change-Id: I1a706d028a9ca894348a19b7b3df1ea673e4ec90
    Partial-Bug: #1790721