TLMigrateInstance: Fix live migration breakage
Commit 77fcff4 unintentionally incorporated code from
TLMigrateInstance.CheckPrereq into TLMigrateInstance._RunAllocator, presumably
during a rebase from earlier versions of the patch to the 2.5 codebase. As a
result all migrations running without an iallocator were performed non-live :-(
This patch moves the affected code back to CheckPrereq.
Signed-off-by: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>