Fix getting configuration filter for exotics only

We need to respect the original list of labels not just take the
exotics. There might be some exotics that are not in the full
list of labels which thus should be filtered out.

Also make the logic clearer by using sets and set operations.

Author: vpodzime

build-scripts/get_labels_expr.py

@@ -39,16 +39,20 @@ def get_labels_from_file(f_path):
             yield label
 
 def main(labels_f_path, exotics_f_path, run_on_exotics, only_exotics):
+    all_labels = set()
+    exotics = set()
+    for label in get_labels_from_file(labels_f_path):
+        all_labels.add(label.strip())
+    for label in get_labels_from_file(exotics_f_path):
+        exotics.add(label.strip())
+
     labels_to_run = set()
     if only_exotics:
-        for label in get_labels_from_file(exotics_f_path):
-            labels_to_run.add(label.strip())
+        labels_to_run = all_labels.intersection(exotics)
+    elif not run_on_exotics:
+        labels_to_run = all_labels.difference(exotics)
     else:
-        for label in get_labels_from_file(labels_f_path):
-            labels_to_run.add(label.strip())
-        if not run_on_exotics:
-            for label in get_labels_from_file(exotics_f_path):
-                labels_to_run.discard(label.strip())
+        labels_to_run = all_labels
 
     print("(", end="")
     labels_eqs = ('label == "%s"' % label for label in sorted(labels_to_run))