virkmodtest: Don't fail if modprobe doesn't exist
virkmodtest: Don't fail if modprobe doesn't exist

On some very basic installations (e.g. some container images) the
modprobe binary might be missing. If that is the case, don't fail
virkmodtest.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,eskultety/libvirt,eskultety/libvirt,zippy2/libvirt,crobinso/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,crobinso/libvirt,andreabolognani/libvirt,nertpinx/libvirt,eskultety/libvirt,zippy2/libvirt,fabianfreyer/libvirt,eskultety/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,fabianfreyer/libvirt,libvirt/libvirt,jardasgit/libvirt,jardasgit/libvirt,andreabolognani/libvirt,eskultety/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,andreabolognani/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,libvirt/libvirt,jfehlig/libvirt,crobinso/libvirt