virfile: Report error when changing pipe size fails

virfile: Report error when changing pipe size fails

When changing the size of pipe that virFileWrapperFdNew() creates
we start at 1MiB and if that fails because it's above the system
wide limit we get EPERM and continue with half of the size.

However, we might get another error in which case we should
report proper system error and return failure from
virFileWrapperFdNew().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>