Do not print btrfs error in log
Do not print btrfs error in log

Btrfs error are pretty confusing while reading CI logs, while they
are pretty normal to have in case provided directories are not btrfs ones
While this won't be an issue for CentOS 8 which do not have btrfs binary
Ubuntu would claim that provided directories are not btrfs ones or even
do not exist.

Change-Id: I1b932877b1dc57d065e9eebc7cbd20712515efd5
Related-Bug: #1855754

stackforge/os-ansible-deployment,openstack/openstack-ansible,stackforge/os-ansible-deployment,openstack/openstack-ansible