[upgrade] Rebalance in MH node to 5.0.x hang

Steps to reproduce:

• Install Couchbase server 5.0.0 on 6 centos server 7.6
• Create 6 nodes cluster with services (2 kv [224,239], 2 index [167,225] and 2 n1ql [226,227])
• Create default bucket and load 1K docs to bucket.
• Offline upgrade node 2 nodes (kv 239 and index 167) to 6.5.0-4931. Offline upgrade went well.
• Install Couchbase server 6.5.0-4931 on a new centos 7.6 server (210)
• Add node 210 with kv service to mix version cluster above.
• Rebalance. Rebalance hang after few seconds running.

Did another run, the last stable build is 4918