update CI workflows: update/fix codecheck; remove Ubuntu 18.04 (#1167)

1. update/fix codecheck

Run workflow with pylint 2.15.7

Add a  bunch of fiddly and mostly cosmetic changes to
make pylint (and make codecheck) happy.

Also try to run pyflakes3 vs. pyflakes

2. remove Ubuntu 18.04

Ubuntu 18.04 has been removed from github actions, so
we remove it from our workflow as well

examples/consoles.py

@@ -69,7 +69,10 @@ class Console( Frame ):
         self.bindEvents()
         self.sendCmd( 'export TERM=dumb' )
 
-        self.outputHook = None
+        def outputHook( _obj, _text):
+            return True
+
+        self.outputHook = outputHook
 
     def makeWidgets( self ):
         "Make a label, a text area, and a scroll bar."
@@ -111,10 +114,8 @@ class Console( Frame ):
         self.text.insert( 'end', text )
         self.text.mark_set( 'insert', 'end' )
         self.text.see( 'insert' )
-        outputHook = lambda x, y: True  # make pylint happier
-        if self.outputHook:
-            outputHook = self.outputHook
-        outputHook( self, text )
+        if callable( self.outputHook ):
+            self.outputHook( self, text )
 
     def handleKey( self, event ):
         "If it's an interactive command, send it to the node."
@@ -294,10 +295,10 @@ class ConsoleApp( Frame ):
             'switches': 'Switch',
             'controllers': 'Controller'
         }
-        for name in titles:
+        for name, title in titles.items():
             nodes = getattr( net, name )
             frame, consoles = self.createConsoles(
-                cframe, nodes, width, titles[ name ] )
+                cframe, nodes, width, title )
             self.consoles[ name ] = Object( frame=frame, consoles=consoles )
         self.selected = None
         self.select( 'hosts' )