Remove duplicate implementation of tobool

This patch removes the duplicate tobool function from hooking.py,
and replace it with utils.tobool.

Change-Id: Ie0d382dabc9df68139070e8ac10f84ba1ca3774b
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/8446
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>