nodedev: refactor mdevctl thread functions

nodedev: refactor mdevctl thread functions

Factor out a new scheduleMdevctlUpdate() function so that we can re-use
it from other places. Now that other events can make it necessary to
re-query mdevctl for mdev updates, this function will be useful for
coalescing multiple updates in quick succession into a single mdevctl
query.

Also rename a couple functions. The names weren't very descriptive of
their behavior. For example, the old scheduleMdevctlHandler() function
didn't actually schedule anything, it just started a thread. So rename
it to free up the 'schedule' name for the above refactored function.

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