bindingXMLRPC: Log unhandled exception for new Thread

Adding a traceback log for unhandled exceptions when execute
start in BindingXMLRPC class so it will not die silently.

Change-Id: I2861f1caad84d29d8cbca39613a0ad3f061a3b0c
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23082
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>