Update documentation for commands with specific output formats on sharded cluster

Original Description

The documentation at https://docs.mongodb.com/manual/reference/command/collMod/#change-expiration-value-for-indexes shows the result document as:

{ "expireAfterSeconds_old" : 1800, "expireAfterSeconds_new" : 3600, "ok" : 1 }

We expect this format for the https://docs.mongodb.com/php-library/master/reference/method/MongoDBDatabase-modifyCollection/ method. However, we are adding additional topologies for our tests, and noticed that with a sharded cluster, the output format changes to:

{

	"raw" : {

		"localhost:4100" : {

			"ok" : 0,

			"errmsg" : "ns does not exist",

			"code" : 26,

			"codeName" : "NamespaceNotFound"

		},

		"localhost:4200" : {

			"expireAfterSeconds_old" : NumberLong(500),

			"expireAfterSeconds_new" : 700,

			"ok" : 1

		}

	},

	"ok" : 1,

	"operationTime" : Timestamp(1534859095, 4),

	"$clusterTime" : {

		"clusterTime" : Timestamp(1534859095, 4),

		"signature" : {

			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),

			"keyId" : NumberLong(0)

		}

	}

}

Could you please document this difference?

Documentation Summary

Based on this comment, update any command that uses the appendRawResponses helper to include a Behavior section that discusses the output format when executed on a mongos. 

Scope of changes

For 4.2 docs, update the following commands with the behavior section as noted above:

• abortTransaction
• collMod
• createIndexes
• dbStats
• dropIndexes

For 4.0 docs, update the following commands with the behavior section as noted above:

• abortTransaction
• collMod
• createIndexes
• dbStats
• dropIndexes
• reIndex

For 3.6 docs, update the following commands with the behavior section as noted above:

• collMod
• createIndexes
• dbStats
• dropIndexes
• reIndex