qemuProcessBuildDestroyHugepagesPath: Don't warn on destroying non-existent path

qemuProcessBuildDestroyHugepagesPath: Don't warn on destroying non-existent path

This function is called unconditionally from qemuProcessStop to
make sure we leave no dangling dirs behind. However, whenever the
directory we want to rmdir() is not there (e.g. because it hasn't
been created in the first place because domain doesn't use
hugepages at all), we produce a warning like this:

2017-06-20 15:58:23.615+0000: 32638: warning :
qemuProcessBuildDestroyHugepagesPath:3363 : Unable to remove
hugepage path: /dev/hugepages/libvirt/qemu/1-instance-00000001
(errno=2)

Fix this by not producing the warning on ENOENT.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>