Stop looping if all workers have died

If the workers are crashing and the restart limit has been met,
we need to stop listening for events and trigger an internal
error.

testing/acceptance_test.py

@@ -701,6 +701,17 @@ class TestNodeFailure:
             "*2 failed*2 passed*",
         ])
 
+    def test_max_slave_restart_die(self, testdir):
+        f = testdir.makepyfile("""
+            import os
+            os._exit(1)
+        """)
+        res = testdir.runpytest(f, '-n4', '--max-slave-restart=0')
+        res.stdout.fnmatch_lines([
+            "*Unexpectedly no active workers*",
+            "*INTERNALERROR*"
+        ])
+
     def test_disable_restart(self, testdir):
         f = testdir.makepyfile("""
             import os