nodedev: driver: Swap virMdevctlStart and virMdevctlCreate

nodedev: driver: Swap virMdevctlStart and virMdevctlCreate

"start" in libvirt means - "take this object and create an
instance out of it"

"create" in libvirt most of the time means - "take and XML description,
make an object out of it and use it to create an instance"

This gets confusing with mdevctl which uses "start" for both. So, this
patch proposes to use virMdevctlStart in cases where from libvirt's POV
we're starting a defined device (unlike mdevctl). Similarly, use
virMdevctlCreate in scenarios where XML description is passed to
libvirt and a transient device is supposed to be created.

Signed-off-by: Erik Skultety <eskultet@redhat.com>
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>