mm: numa: Account for failed allocations and isolations as migration failures

Subject says it all. Allocation failures and a failure to isolate should
be accounted as a migration failure. This is partially another
difference between base page and transhuge page migration. A base page
migration makes multiple attempts for these conditions before it would
be accounted for as a failure.

Signed-off-by: Mel Gorman <mgorman@suse.de>