api: add virNodeDeviceUpdate()

api: add virNodeDeviceUpdate()

A public API method which allows to update or modify objects is
implemented for almost all other objects that have a concept of
persistent definition and activatability. Currently node devices of type
mdev can be persistent and active. This new method allows to update
defined and active node devices as well.

Signed-off-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>