Provide a reference to the previous instance in case of events
Provide a reference to the previous instance in case of events

When retrieving instance events, the old WMI library provides the
previous instance state as well, when available.

This patch ensures we set this attribute as well, maintaining
compatibility with the old library.

alinbalutoiu/PyMI,cloudbase/PyMI,alinbalutoiu/PyMI,alinbalutoiu/PyMI,cloudbase/PyMI,cloudbase/PyMI