vdsm.utils: drop unused ImagePathStatus and getPidNiceness

Change-Id: I78a732c6204385a3c33c4a1aea2cc78e3f404bb6
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20674
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Petr Šebek <psebek@redhat.com>
Tested-by: Petr Šebek <psebek@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>