[Magma] kv swap rebalance hung while fts index building

Build: 7.1.0 build 1047

Tests:
centos-fts_moving-topology_4.5_P0
./testrunner -i /tmp/testexec.69742.ini -p get-cbcollect-info=False,disable_HTP=True,index_type=upside_down,get-logs=False,stop-on-failure=False,GROUP=P0,fts_quota=990,get-cbcollect-info=False,bucket_storage=magma,enable_dp=True -t fts.moving_topology_fts.MovingTopFTS.swap_rebalance_kv_during_index_building,items=30000,cluster=D,F,replicas=0,GROUP=P0,get-cbcollect-info=False,disable_HTP=True,index_type=upside_down,get-logs=False,stop-on-failure=False,fts_quota=990,bucket_storage=magma,enable_dp=True

./testrunner -i /tmp/testexec.69742.ini -p get-cbcollect-info=False,disable_HTP=True,index_type=upside_down,get-logs=False,stop-on-failure=False,GROUP=P0,fts_quota=990,get-cbcollect-info=False,bucket_storage=magma,enable_dp=True -t fts.moving_topology_fts.MovingTopFTS.failover_master_during_index_building,items=30000,cluster=D,D+F,GROUP=P0,get-cbcollect-info=False,disable_HTP=True,index_type=upside_down,get-logs=False,stop-on-failure=False,fts_quota=990,bucket_storage=magma,enable_dp=True

Test steps:

• 2 node Cluster with data, search
• Create a bucket (magma as storage backend) with 30000 docs
• Create a default FTS index
• While the above index building, swap rebalance data node
• Rebalance hangs

172.23.97.211 is the outgoing node
172.23.96.141 is the incoming node

Logs:

https://cb-jira.s3.us-east-2.amazonaws.com/logs/hung/collectinfo-2021-07-07T200857-ns_1%40172.23.96.141.zip
https://cb-jira.s3.us-east-2.amazonaws.com/logs/hung/collectinfo-2021-07-07T200857-ns_1%40172.23.97.211.zip
https://cb-jira.s3.us-east-2.amazonaws.com/logs/hung/collectinfo-2021-07-07T200857-ns_1%40172.23.97.212.zip