beam.smp memory usage grows to 2 GB when xdcr feature is enabled and rebalancing is in progress

- Created default buckets on a 2:2 cluster
        [10.1.3.235, 10.1.3.236] : [10.1.3.237, 10.1.3.238]
- Set up bidirectional replication for the bucket, ran load on both the buckets.
- Swap rebalanced a node on both clusters
        [10.1.3.235, 10.3.2.54] : [10.1.3.237, 10.3.2.55]
- Upon completion of rebalance, stopped load on default buckets.
- Created standard buckets on both the clusters.
- Set up unidirectional replication for the standard bucket from cluster 1 to cluster 2, ran load on cluster 1.
- Stopped load after a point.
- With replication still going on, Rebalance-in the removed nodes on each cluster (to make it 3:3)
        [10.1.3.235, 10.3.2.54, 10.1.3.236] : [10.1.3.237, 10.3.2.55, 10.1.3.238]
- During rebalance, load is not going on on either cluster, however replication is still going on.
        - Heavy swap on the orchestrators of both the clusters
        - Erlang using up a lot of memory ( > 2.5G )
- Rebalance gradually completed on cluster 2.
- Rebalance fails on cluster 1:

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Rebalance exited with reason {{badmatch,{error,timeout}},
{gen_server,call,
[{'ns_memcached-bucket','ns_1@10.1.3.235'},
{get_vbucket,835},
60000]}}
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- If tried to re-rebalance, rebalance fails again:

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Rebalance exited with reason {not_all_nodes_are_ready_yet,['ns_1@10.1.3.235']}
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- This is probably because, 10.1.3.235 is in "PEND" state on the UI.

- Uploading grabbed diags onto s3.

https://s3.amazonaws.com/bugdb/MB-6649/10.1.3.235-8091-diag.txt.gz
https://s3.amazonaws.com/bugdb/MB-6649/10.1.3.236-8091-diag.txt.gz
https://s3.amazonaws.com/bugdb/MB-6649/10.3.2.54-8091-diag.txt.gz
https://s3.amazonaws.com/bugdb/MB-6649/10.1.3.237-8091-diag.txt.gz
https://s3.amazonaws.com/bugdb/MB-6649/10.1.3.238-8091-diag.txt.gz
https://s3.amazonaws.com/bugdb/MB-6649/10.3.2.55-8091-diag.txt.gz