Limit number of instances to test to 2 (refs #20760).

tester.py

@@ -49,6 +49,7 @@ class Tester():
     VALID_ARGS = ['-e', '-f', '-b', '-d', '-h']
     MAX_LOG_FILES = 50
     NO_MAIL_FAILURES_COUNT = 30
+    MAX_INSTANCES = 2
 
     def __init__(self, *args):
         log('\033[96m-------------------------------\033[0m')
@@ -147,6 +148,8 @@ class Tester():
                 ms_users.append(user)
         # Get MediaServer tests
         if ms_users:
+            if len(ms_users) > self.MAX_INSTANCES:
+                ms_users = ms_users[:self.MAX_INSTANCES]
             # Clone testing suite
             ms_path = os.path.join(path, 'ms-testing-suite')
             if os.path.exists(ms_path):