Futzing with read preference (#3963)

* allow setting readpreference when using rest api.

* take out partially complete unit test.

* oops. nit

* Include read preference option for find directly from api and adding few more tests

* Adding catch for all tests

* Keep same check for get and find

* Turn read preference case insensitive

* Includes and subqueries read preferences through API

* Fixing bugs regarding changes that were done in master branch during the last year

* Changing behavior to make includeReadPreference and subqueryReadPreference to follow readPreference by default

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -926,6 +926,9 @@ export class MongoStorageAdapter implements StorageAdapter {
   }
 
   _parseReadPreference(readPreference: ?string): ?string {
+    if (readPreference) {
+      readPreference = readPreference.toUpperCase();
+    }
     switch (readPreference) {
       case 'PRIMARY':
         readPreference = ReadPreference.PRIMARY;