cli: add missing return 0s to various handlers

Should silence LGTM's [py/procedure-return-value-used] warnings.

sopel/cli/config.py

@@ -95,6 +95,8 @@ def handle_list(options):
             name, _ = os.path.splitext(config_filename)
             print(name)
 
+    return 0  # successful operation
+
 
 def handle_init(options):
     """Use config wizard to initialize a new configuration file for the bot
@@ -123,6 +125,7 @@ def handle_init(options):
 
     print('Starting Sopel config wizard for: %s' % config_filename)
     utils.wizard(config_name)
+    return 0  # successful operation
 
 
 def handle_get(options):
@@ -147,6 +150,7 @@ def handle_get(options):
 
     # Display the value
     print(settings.get(section, option))
+    return 0  # successful operation
 
 
 def main():

sopel/cli/plugins.py

@@ -223,6 +223,8 @@ def handle_list(options):
 
         print(template.format(**description))
 
+    return 0  # successful operation
+
 
 def handle_show(options):
     """Show plugin details"""
@@ -271,6 +273,7 @@ def handle_show(options):
     print('Setup:', 'yes' if plugin.has_setup() else 'no')
     print('Shutdown:', 'yes' if plugin.has_shutdown() else 'no')
     print('Configure:', 'yes' if plugin.has_configure() else 'no')
+    return 0  # successful operation
 
 
 def handle_configure(options):
@@ -305,6 +308,8 @@ def handle_configure(options):
             "Use 'sopel-plugins enable {0}' to enable it".format(plugin_name)
         )
 
+    return 0  # successful operation
+
 
 def _handle_disable_plugin(settings, plugin_name, force):
     excluded = settings.core.exclude