Add a server, Remove it, Add it again leaves incorrect state

build 1.6.0a-57

• join 2 servers A & B and Rebalance

• next, do a Pending Remove on server B and Rebalance

at this point...

• server A correctly just shows server A in server A's web UI

• server B correctly goes back to initial-config-wizard

next...

• in server B, join back to server A

at this point, server B is incorrectly listed already as an Active Server

instead, server B should be listed on the Pending Rebalance tab (in a Pending Add state).