Replace pylint with pyflakes/flake8

pylint reports a lot of warnings, but many of them are false positive,
and it's difficult to configure it. It also seems that for some reason
the included config file is not working well with the latest version.

Update the documentation to recommend using pyflakes and flake8 instead
of pylint. Remove the pylint config and add a basic flake8 config with
minimum settings:

- Maximum line length 80 columns
- Ignore warnings about indentation (repo uses 2 rather than expected 4)
- Ignore warnings about import placement

In this commit no code cleanup is done, and it's expected that most of
the files will throw up quite a few warnings, at least for flake8. These
can be cleaned up in follow-up commits.

The existing pylint suppression comments are left as-is. These will be
helpful when cleaning up pyflakes warnings later.

Change-Id: I2f7cb4340266ed07cc973ca6483b8f09d66a765b
diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..45ab656
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,3 @@
+[flake8]
+max-line-length=80
+ignore=E111,E114,E402