ms_amarisoft: fix various regressions

this patch fixes some regressions in the Amarisoft UE class,
the config template, etc. that have been undetected bc we never
executed tests with it.

Change-Id: I397e675a4018acf3372a3b7e29fd864703b2b919
diff --git a/src/osmo_gsm_tester/obj/ms.py b/src/osmo_gsm_tester/obj/ms.py
index 70ce558..7257769 100644
--- a/src/osmo_gsm_tester/obj/ms.py
+++ b/src/osmo_gsm_tester/obj/ms.py
@@ -36,6 +36,11 @@
         }
     schema.register_resource_schema('modem', resource_schema)
 
+    config_schema = {
+        'count': schema.UINT
+        }
+    schema.register_config_schema('modem', config_schema)
+
 class MS(log.Origin, metaclass=ABCMeta):
     """Base for everything about mobile/modem and SIMs."""
 
@@ -125,3 +130,6 @@
 
     def get_counter(self, counter_name):
         raise log.Error('get_counter() not implemented!')
+
+    def features(self):
+        return self._conf.get('features', [])