nodedev: add an active config to mdev

nodedev: add an active config to mdev

The configuration of a defined mdev can be modified after the mdev is
started. The defined configuration and the active configuration can
therefore run out of sync. Handle this by storing the modifiable data
which is the mdev type and attributes in two separate active and
defined configurations. mdevctl supports with callout scripts to do an
attribute retrieval of started mdevs which is already implemented in
libvirt.

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