Gmoshkin/fix expel

Summary

• refactor: use column_name! macro to see where we modify particular global table columns

• test: add a failing test for bucket rebalancing before instance expel

• fix: do not expel instance until replicaset master is switched over

• fix: expelled instance used to not know it was expelled

• refactor: cleanup conf change code

• test: expel tests were broken

• test: bump timeouts to reduce potential flakiness

• fix: don't persist local component of promotion vclock

• chore: cleanup formatting

• refactor: rename src/governor/{cc -> conf_change}.rs

• test: reduce test_ddl_create_table_unfinished_from_snapshot flakiness

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• Part of #856 (closed)
• Cherry-pick to: none
• Docs follow-up: not necessary