adjust number of domains in cpupools when destroying domain

adjust number of domains in cpupools when destroying domain

Commit bac6334b51d9bcfe57ecf4a4cb5288348fcf044a (move domain to
cpupool0 before destroying it) introduced an error in the accounting
of cpupools regarding the number of domains. The number of domains
is nor adjusted when a domain is moved to cpupool0 in kill_domain().

Correct this by introducing a cpupool function doing the move
instead of open coding it by calling sched_move_domain().

Reported-by: Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>
Reviewed-by: Andrew Cooper <Andrew.Cooper3@citrix.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>