Since 86d90b3a (yes, my patch; again) we are supporting NBD storage
migration. However, on error recovery path we got the steps reversed.
The correct order is: return NBD port to the virPortAllocator and then
either unlock the vm or remove it from the driver. Not vice versa.

==11192== Invalid write of size 4
==11192==    at 0x11488559: qemuMigrationPrepareAny (qemu_migration.c:2459)
==11192==    by 0x11488EA6: qemuMigrationPrepareDirect (qemu_migration.c:2652)
==11192==    by 0x114D1509: qemuDomainMigratePrepare3Params (qemu_driver.c:10332)
==11192==    by 0x519075D: virDomainMigratePrepare3Params (libvirt.c:7290)
==11192==    by 0x1502DA: remoteDispatchDomainMigratePrepare3Params (remote.c:4798)
==11192==    by 0x12DECA: remoteDispatchDomainMigratePrepare3ParamsHelper (remote_dispatch.h:5741)
==11192==    by 0x5212127: virNetServerProgramDispatchCall (virnetserverprogram.c:435)
==11192==    by 0x5211C86: virNetServerProgramDispatch (virnetserverprogram.c:305)
==11192==    by 0x520A8FD: virNetServerProcessMsg (virnetserver.c:165)
==11192==    by 0x520A9E1: virNetServerHandleJob (virnetserver.c:186)
==11192==    by 0x50DA78F: virThreadPoolWorker (virthreadpool.c:144)
==11192==    by 0x50DA11C: virThreadHelper (virthreadpthread.c:161)
==11192==  Address 0x1368baa0 is 576 bytes inside a block of size 688 free'd
==11192==    at 0x4A07F5C: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==11192==    by 0x5079A2F: virFree (viralloc.c:580)
==11192==    by 0x11456C34: qemuDomainObjPrivateFree (qemu_domain.c:267)
==11192==    by 0x50F41B4: virDomainObjDispose (domain_conf.c:2034)
==11192==    by 0x50C2991: virObjectUnref (virobject.c:262)
==11192==    by 0x50F4CFC: virDomainObjListRemove (domain_conf.c:2361)
==11192==    by 0x1145C125: qemuDomainRemoveInactive (qemu_domain.c:2087)
==11192==    by 0x11488520: qemuMigrationPrepareAny (qemu_migration.c:2456)
==11192==    by 0x11488EA6: qemuMigrationPrepareDirect (qemu_migration.c:2652)
==11192==    by 0x114D1509: qemuDomainMigratePrepare3Params (qemu_driver.c:10332)
==11192==    by 0x519075D: virDomainMigratePrepare3Params (libvirt.c:7290)
==11192==    by 0x1502DA: remoteDispatchDomainMigratePrepare3Params (remote.c:4798)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>