Add a wait baseline when looking up registry values (elastic#8216) (e…

…lastic#8239)

With the nature of VMs and disk, writing or reading a file can be out of sync.
Instead of only sleeping only the windows case we sleep on every tested
platform before asserting the content of the registry.

closes elastic#8102

(cherry picked from commit ca78d74)

filebeat/tests/system/test_registrar.py

@@ -809,9 +809,8 @@ def test_clean_inactive(self):
             lambda: self.log_contains_count("Registry file updated") > 1,
             max_timeout=15)
 
-        if os.name == "nt":
-            # On windows registry recreation can take a bit longer
-            time.sleep(1)
+        # Syncing file on disk is always susceptible to timing issues.
+        time.sleep(1)
 
         data = self.get_registry()
         assert len(data) == 2