sched: adjustments to some performance counters

sched: adjustments to some performance counters

More specifically:

1) rename vcpu_destroy to vcpu_remove

It seems this have had to be done as part of 7e6b926a
("cpupools: Make interface more consistent"), which
renamed the function but not the counter.

In fact, because of cpupools, vcpus are not only removed
from a scheduler when they are destroyed, but also when
domains move between pools.

Make the related statistics counter reflect that more
properly.

2) rename vcpu_init to vcpu_alloc

As it lives in *_alloc_vdata.

3) add vcpu_insert

matching vcpu_remove, and useful to quickly check
whether the number of insertions and removal matches,
or in general investigare their relationship.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>