fix handling of StructOf datatype

- change secop.client.SecopClient to use native types instead of
  strings for its setParameter and execCommand methods.
- secop-gui: for now, setParameter accept strings for complex types.
  this should be changed to use native type in an other change
- fix bugs in parser.py

+ SecopClient: make visible in an error message that the error
  was generated on the SEC node
+ fix a bug when a command is called with 0 as argument

Change-Id: Id87d4678311ef8cf43a25153254d36127e16c6d9
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/23299
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/gui/mainwindow.py

@@ -75,14 +75,16 @@ class QSECNode(QObject):
         return self.modules[module]['parameters'][parameter]
 
     def setParameter(self, module, parameter, value):
-        self.conn.setParameter(module, parameter, value)
+        # TODO: change the widgets for complex types to no longer use strings
+        datatype = self.conn.modules[module]['parameters'][parameter]['datatype']
+        self.conn.setParameter(module, parameter, datatype.from_string(value))
 
     def getParameter(self, module, parameter):
         return self.conn.getParameter(module, parameter, True)
 
-    def execCommand(self, module, command, arg):
+    def execCommand(self, module, command, argument):
         try:
-            return self.conn.execCommand(module, command, arg)
+            return self.conn.execCommand(module, command, argument)
         except Exception as e:
             return 'ERROR: %r' % e, {}