fix(serverSelection): make sure to pass session to serverSelection

The executeWithSelection changes failed to pass the session to
server selection, which broke mongos pinning. This ensures that
we pass a session to serverSelection.

lib/operations/execute_operation.js

@@ -132,6 +132,11 @@ function executeWithServerSelection(topology, operation, callback) {
     return;
   }
 
+  const serverSelectionOptions = {
+    readPreference,
+    session: operation.session
+  };
+
   function callbackWithRetry(err, result) {
     if (err == null) {
       return callback(null, result);
@@ -142,7 +147,7 @@ function executeWithServerSelection(topology, operation, callback) {
     }
 
     // select a new server, and attempt to retry the operation
-    topology.selectServer(readPreference, (err, server) => {
+    topology.selectServer(serverSelectionOptions, (err, server) => {
       if (err || !supportsRetryableReads(server)) {
         callback(err, null);
         return;
@@ -153,7 +158,7 @@ function executeWithServerSelection(topology, operation, callback) {
   }
 
   // select a server, and execute the operation against it
-  topology.selectServer(readPreference, (err, server) => {
+  topology.selectServer(serverSelectionOptions, (err, server) => {
     if (err) {
       callback(err, null);
       return;