GUI fixes

- do not show command result dialog when result is None
- apply fmtstr, if available

+ fix io import in secop.core
+ change old style <basecls>.__init__(self, ...) calls to super().__init__(...)

Change-Id: I599d5d8e8ff430ea9454a0858d703290e87454fc
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/26397
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Jens Krueger <jens.krueger@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/gui/mainwindow.py

@@ -44,7 +44,7 @@ class QSECNode(QObject):
     logEntry = pyqtSignal(str)
 
     def __init__(self, uri, parent=None):
-        QObject.__init__(self, parent)
+        super().__init__(parent)
         self.conn = conn = secop.client.SecopClient(uri)
         conn.validate_data = True
         self.log = conn.log
@@ -83,10 +83,7 @@ class QSECNode(QObject):
         return self.conn.getParameter(module, parameter, True)
 
     def execCommand(self, module, command, argument):
-        try:
-            return self.conn.execCommand(module, command, argument)
-        except Exception as e:
-            return 'ERROR: %r' % e, {}
+        return self.conn.execCommand(module, command, argument)
 
     def queryCache(self, module):
         return {k: Value(*self.conn.cache[(module, k)])
@@ -115,7 +112,7 @@ class QSECNode(QObject):
 
 class MainWindow(QMainWindow):
     def __init__(self, hosts, parent=None):
-        super(MainWindow, self).__init__(parent)
+        super().__init__(parent)
 
         loadUi(self, 'mainwindow.ui')