Add --no-loadscope-reorder and --loadscope-reorder options (#1217)

Based on #1098.

Closes #1098

---------

Co-authored-by: Toan Vuong <toan.vuong@hyperscience.com>

src/xdist/scheduler/loadscope.py

@@ -371,11 +371,15 @@ class LoadScopeScheduling:
             work_unit = unsorted_workqueue.setdefault(scope, {})
             work_unit[nodeid] = False
 
-        # Insert tests scopes into work queue ordered by number of tests.
-        for scope, nodeids in sorted(
-            unsorted_workqueue.items(), key=lambda item: -len(item[1])
-        ):
-            self.workqueue[scope] = nodeids
+        if self.config.option.loadscopereorder:
+            # Insert tests scopes into work queue ordered by number of tests.
+            for scope, nodeids in sorted(
+                unsorted_workqueue.items(), key=lambda item: -len(item[1])
+            ):
+                self.workqueue[scope] = nodeids
+        else:
+            for scope, nodeids in unsorted_workqueue.items():
+                self.workqueue[scope] = nodeids
 
         # Avoid having more workers than work
         extra_nodes = len(self.nodes) - len(self.workqueue)