When running without that option, the list of servers might be empty, resulting in leftover instances on the host that is about to be migrated. Change-Id: I85915f0f86655f3a1eb5f54911d24e4e0e75f340
Forward-ported from Train commit I19c7f05b538a7abc9253194bf041c037b1998378. Change-Id: If07b84e0bbdcb7da8dbef87cc8826987f1d11cf8