Comment 18 for bug 1790721

Reviewed: https://review.openstack.org/600119
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ff8cb33283bbce474426f20f21675ecc1449b4d7
Submitter: Zuul
Branch: stable/ocata

commit ff8cb33283bbce474426f20f21675ecc1449b4d7
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.

    Conflicts:
          nova/cmd/status.py

    NOTE(mriedem): The conflict is due to not having change
    I35206e665f2c81531a2269dd66f8c5c0df834245 in Ocata.

    Change-Id: I1a706d028a9ca894348a19b7b3df1ea673e4ec90
    Partial-Bug: #1790721
    (cherry picked from commit dcd421ae9e6f0391fea06c9d20949267354c3b3c)
    (cherry picked from commit f588a0b6c337368596bc8732141e864f56f72212)
    (cherry picked from commit 6a806de71b945509c8c5d3de53ff7ba5aa75bf87)
    (cherry picked from commit 3f562226112b99d2044dd05a2e15b9752d5c9c1d)