Comment 3 for bug 1621818

I've submitted a patch to fix this issue: https://review.openstack.org/#/c/368590/

With this patch, we put the execute call in a try, except block to catch possible errors. It also logs a warning with the path and error message.

Now, at least once, the update will succeed.

Logs now show:
2016-09-09 17:10:22.033 22753 WARNING nova.virt.libvirt.utils [req-a8b01dc3-f349-44ba-85ef-2ef87b0d7eb6 9bded406068d46c5b817a1f7b604dd89 028894d76a79489ead5d682232ecbe83 - - -] Failed to update mtime on path /var/lib/nova/instances/_base/79e34519bacb47ad6f64c4baca4d33fd5c57d34d: Unexpected error while running command.
Command: sudo nova-rootwrap /etc/nova/rootwrap.conf touch -c /var/lib/nova/instances/_base/79e34519bacb47ad6f64c4baca4d33fd5c57d34d
Exit code: 1
Stdout: u''
Stderr: u"/bin/touch: setting times of '/var/lib/nova/instances/_base/79e34519bacb47ad6f64c4baca4d33fd5c57d34d': Input/output error\n"