virt-host-validate: Report an error if failed to detect CGroups
virt-host-validate: Report an error if failed to detect CGroups

As a part of its checks, virt-host-validate calls virCgroupNew()
to detect CGroup controllers which are then printed out. However,
virCgroupNew() can fail (with appropriate error message set).
Let's print an error onto stderr if that happens.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>
Reviewed-by: Fabiano Fidêncio <d95e9796398a6087d3fb67947e5776c26b264733@fidencio.org>

libvirt/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,nertpinx/libvirt,nertpinx/libvirt,nertpinx/libvirt,crobinso/libvirt,zippy2/libvirt,libvirt/libvirt,nertpinx/libvirt,crobinso/libvirt,zippy2/libvirt,jfehlig/libvirt,nertpinx/libvirt,olafhering/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt