Use ShardingTest to verify that CausalConsistency is supported by shell

• add negative tests verifying that causal consistency is enabled for the commands mentioned in SERVER-28869

  // start a shard that could use read majority
  var st = new ShardingTest({shards:1, mongos:1, rs: {nodes:1, enableMajorityReadConcern: ""}}
  
  // once its started enable causal consistency
  db.setMongo().setCausalConsistency();
  
  // check its enabled using 
  assert.eq(db.getMongo().getCausalConsistency(), true)
  
  // check its enabled for a command (find, aggregate, count etc ) using 
  db.getMongo().isCausalConsistencyEnabled(cmdName) {}
  
  

• add negative tests verifying that causal consistency is not enabled when its not explicitly set or for commands not in the list

• add tests that check that commands work as (using find as an example):

  
  // make sure that operation time is not set 
  assert.isnull(mongo.getOperationTime(), ...)
  
  // make sure that cluster time is not set 
  assert.isnull(mongo.getClusterTime(), ...)
  
  db.runCommand({find:'foo'})
  // make sure that operation time is still not set 
  // make sure that cluster time is set 
  
  
  db.runCommand({insert:'foo', documents:[{x: 1}]})
  // now both cluster and operation time are set
  const time = mongo.getOperationTime()
  
  // increase operation time to one day ahead and run a command
  const time = mongo.setOperationTime(increasedTime)
  db.runCommand({find:'foo'})
  // now it should fail with "Operation time can not be greater than cluster time" error
  
  // use the logical time returned as a new operation time and run the read 
  // the result should match the write and returned operation time must be >= passed operation time