Update except syntax according to pep3110.

The old except BlahException, e: is ambiguous and discouraged going
forward. The new syntax for python 3.x is supported since Python 2.6
and already present in our codebase, so it makes sense to
homogeinize our syntax. For more information:

http://www.python.org/dev/peps/pep-3110/

Change-Id: I2c4ac78dace34a41e1afb9f6560889ad9bd34ddf
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/10942
Reviewed-by: Dan Kenigsberg <danken@redhat.com>