[FTS] MCP: after stop rebalance, rebalancing again doesn't move pindexes due to MCP deadlock

Saw this along the way while diagnosing MB-19040, but by that time had ended up too many button presses to remember.

Roughly, in 3 node cluster-run environment on OSX...

CBFT_ENV_OPTIONS=hideUI=false COUCHBASE_NUM_VBUCKETS=1024 ./cluster_run --nodes=3

Run one of Aruna's scripts....

./testrunner -i MY_CLUSTER.ini -p skip-cleanup=True,get-cbcollect-info=False,get-logs=False,stop-on-failure=False -t fts.moving_topology_fts.MovingTopFTS.node_reboot_only_kv_during_index_building,items=10000,cluster=D,F,F,GROUP=P0

After it's done, start playing around with rebalancing, removing nodes, stopping rebalance, and restarting rebalance. You might see that the pindex layout isn't balanced and attempting to Rebalance again (incorrectly) does not help make the pindex layout balanced again.