qemu_migration: Properly wait for migration to be canceled

qemu_migration: Properly wait for migration to be canceled

In my commit v8.7.0-57-g2d7b22b561 I attempted to make
qemuMigrationSrcCancel synchronous, but failed. When we are canceling
migration after some kind of error which is detected in
in qemuMigrationSrcWaitForCompletion, jobData->status will be set to
VIR_DOMAIN_JOB_STATUS_FAILED regardless on QEMU state. So instead of
relying on the translated jobData->status in qemuMigrationSrcIsCanceled
we need to check the migration status we get from QEMU MIGRATION event.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>