fix issue with alias_config removed at MLZ

rotation_z will be automatically assigned to one of a list
of aliases ('unique' entry in frappy_config) but will complain
when this is not unique.

setups/frappy.py

@@ -34,6 +34,7 @@ devices = dict(
             'targets': {'se_mf': 20},
         },
         rotation_z = {
+            'unique': ['a3', 'om'],
             'alias': 'dom',
             'targets': {'se_om': 20, 'se_stickrot': 19},
             'envlist': False,