Data lost in offline upgrade to MH if 5.x.x cluster initialize with custom data path

Steps to reproduce:

• Install Couchbase server 5.1.0 on 2 centos servers
• Initialize one node with custom path (node s44015.sc.couchbase.com) for data and index (/tmp/data and /tmp/index)
• Create a cluster of 2 nodes and create 3 buckets.
• Load 10K docs to all 3 buckets.
• Offline upgrade on node with custom path, after done with upgrade, node with custom path was reset back to default installation path (/opt/couchbase/var/...)
• All 3 buckets show half of data (5K) due to data path changed (lost 5K docs).
• If all nodes in cluster were set to custom path in 5.x.x, then after upgrade, all data would be gone in all buckets.

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