NFS share not mounted due to findmnt behaviour change

[Lee Yarwood]

Description
===========
The following findmnt behaviour change present in util-linux-2.23.2-33 causes libvirt_utils.is_mounted to incorrectly return True when a share is already mounted on a host but not by Nova, for example in an allinone/devstack environment where cinder-volume is running on the same host and has already mounted the share :

findmnt --target behaviour changed in 7.3, shows all mount-points in chroot
https://bugzilla.redhat.com/show_bug.cgi?id=1405238

Steps to reproduce
==================
- Install devstack with the NFS plugin on a RHEL 7.3, CentOS 7.3 or Fedora 25 host.
- Attempt to launch a volume backed instance.

Expected result
===============
NFS share mounted by both Nova and Cinder allowing the instance to launch correctly.

Actual result
=============
NFS share only mounted by Cinder causing the instance to fail to launch.

Environment
===========
1. Exact version of OpenStack you are running. See the following
   list for all releases: http://docs.openstack.org/releases/

   devstack (master) + devstack-plugin-nfs (master) + CentOS 7.3

2. Which hypervisor did you use?
   (For example: Libvirt + KVM, Libvirt + XEN, Hyper-V, PowerKVM, ...)
   What's the version of that?

   Libvirt + KVM

2. Which storage type did you use?
   (For example: Ceph, LVM, GPFS, ...)
   What's the version of that?

   NFS

3. Which networking type did you use?
   (For example: nova-network, Neutron with OpenVSwitch, ...)

   n/a

Logs & Configs
==============

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/420146
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=86b361d9166200db2174be87214190a29e77f98f
Submitter: Jenkins
Branch: master

commit 86b361d9166200db2174be87214190a29e77f98f
Author: Lee Yarwood <email address hidden>
Date: Fri Jan 13 16:45:32 2017 +0000

    libvirt: workaround findmnt behaviour change

    findmnt as provided by util-linux-2.23.2-33 now returns 0 when --source
    is already mounted on the host under a different mountpoint [1]. This causes
    issues in environments where cinder-volume may have already mounted a
    given NFS share.

    This change works around this behaviour change by using os.path.ismount
    to confirm if the target is already a mountpoint and if a source is
    provided also checking /proc/mounts to confirm that it is mounted at the
    target location.

    [1] https://bugzilla.redhat.com/show_bug.cgi?id=1405238

    Closes-Bug: #1656774
    Change-Id: Id64cc77237bf770a9a75bbf666a54a604ace558c

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/newton
Review: https://review.openstack.org/428743

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 15.0.0.0rc1 release candidate.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Lee Yarwood (<email address hidden>) on branch: stable/newton
Review: https://review.openstack.org/428743