Comment 12 for bug 1855319

Reviewed: https://review.opendev.org/747604
Committed: https://git.openstack.org/cgit/starlingx/openstack-armada-app/commit/?id=7a859890f77560a1c6436b0967fa49c2a249501d
Submitter: Zuul
Branch: r/stx.3.0

commit 7a859890f77560a1c6436b0967fa49c2a249501d
Author: Mingyuan Qi <email address hidden>
Date: Thu Dec 12 02:41:34 2019 +0000

    Check return value of get subnets before iterate for ironic

    With the update of openstack clients within heat image:
    openstack client >= 4.0.0
    neutron client >= 6.14.0
    neturon lib >= 1.29.1

    The command 'openstack network show ${network} -f value -c subnets'
    returns '[]' instead of null string if no subnets found in the
    specific network. This commit adds a check logic to avoid subsequent
    command returns error by using '[]' as subnet input.

    Change-Id: I695e504518e1c884c7d66ecc94c9fa8787ce9752
    Closes-Bug: 1855319
    Signed-off-by: Mingyuan Qi <email address hidden>