Fix peer2peer migration with transient VMs

Fix peer2peer migration with transient VMs

The qemuMigrationConfirm method shouldn't deal with final VM
cleanup, since it can be called from the peer2peer migration,
which expects to still use the 'vm' object afterwards.

Push the cleanup code out of qemuMigrationConfirm, into its
caller, qemuDomainMigrateConfirm3

* src/qemu/qemu_driver.c: Add VM cleanup code to
  qemuDomainMigrateConfirm3
* src/qemu/qemu_migration.c, src/qemu/qemu_migration.h: Remove
  job handling cleanup from qemuMigrationConfirm