correctness: Use new-style class when using @property

Commit 802e88c60c added a @property to few historic old-style classes.
This works when reading the property value, but does not create a
read-only property as it should. To have a read-only property, the class
must be a new-style class (inherit from object). This patch converts
clientIf, Disaptcher and HSM to new-style classes.

For more info see:
https://docs.python.org/2.6/library/functions.html#property

Change-Id: I7ff98ff07832cb8236470071fcc85da3a0cfa2d2
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28720
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>