Address some pylint issues (#1155)

* Address cyclic-import.

* Address redefined-builtin.

* Address redefined-argument-from-local.

* Address many redefined-outer-name.

* Address pointless-string-statement.

* No longer needed due to separate bugfix.

* Address useless-return.

* Address possibly-used-before-assignment.

* Add TODOs.

* Address super-init-not-called.

* Address function-redefined.

* Address unspecified-encoding.

* Clean up more imports.

plugins/connection/docker.py

@@ -425,11 +425,13 @@ class Connection(ConnectionBase):
                             + to_native(become_output)
                         )
 
+                    chunk = None
                     for key, event in events:
                         if key.fileobj == p.stdout:
                             chunk = p.stdout.read()
                         elif key.fileobj == p.stderr:
                             chunk = p.stderr.read()
+                    # TODO: avoid chunk being set multiple times!
 
                     if not chunk:
                         stdout, stderr = p.communicate()