test/mm.py: Do not die if cromo or momdemmanager is not running

test/mm.py

Index: test/mm.py
diff --git a/test/mm.py b/test/mm.py
index dfdb0a092bed0451a8add1c3ef027d13ba819641..61d5f60251378bfeb7101fbef7ff10da1ce0d550 100755
--- a/test/mm.py
+++ b/test/mm.py
@@ -98,7 +98,13 @@ def EnumerateDevices(manager=None):
   if manager:
     managers = [manager]
   else:
-    managers = [ModemManager(x) for x in MMPROVIDERS]
+    managers = []
+    for provider in MMPROVIDERS:
+      try:
+        managers.append(ModemManager(provider))
+      except dbus.exceptions.DBusException, e:
+        if e._dbus_error_name != 'org.freedesktop.DBus.Error.ServiceUnknown':
+           raise
 
   result = []
   for m in managers: