rebalance should not be allowed when cbrecovery is stopped by REST API or has not completed

Found in build-3.0.0-973-release

Setup: Two clusters: src and dst with 3 nodes each. Please have 2 spare nodes

• Setup xdcr between src and dst cluster
• Ensure xdcr is setup and complete
• Hard Failover two nodes from dst cluster
• Verify nodes failover
• Add two spare nodes in dst cluster
• Initiate cbrecovery from src to dst
• stop cbrecovery using REST API
  http://10.3.121.106:8091//pools/default/buckets/default/controller/stopRecovery?recovery_uuid=3ad71c7b3365593e0979da34306fb2a5

• initiate rebalance operation on dst cluster.

Observations: rebalance operation starts.
Expectation: Since rebalance operation is disallowed from UI when recovery is ongoing (or halted). The rebalance should not be allowed from REST or cli interfaces.