Fix flake8 failures

Fix flake8 failures when running tox and add a note in the README to run
tox for testing patches.

Reviewed By: tnfchris

Differential Revision: https://reviews.llvm.org/D112304

Author: Thomas Preud'homme

README.md

@@ -16,3 +16,9 @@ The infrastructure has the following layout:
  $ROOT/tests - Tests for the infrastructure.
 
 For more information, see the web documentation, or docs/.
+
+Testing
+=======
+
+Testing is done by running tox from the top-level directory. It runs the tests
+for both Python 2 and Python 3, it also checks code style.

lnt/formats/__init__.py

@@ -10,7 +10,7 @@
 from __future__ import absolute_import
 from typing import List, Dict
 try:
-    from plistlib import readPlist
+    from plistlib import readPlist  # noqa: F401  # used to test exception
     from .PlistFormat2 import format as plist  # for Python 2
 except ImportError:
     from .PlistFormat import format as plist  # for Python 3

lnt/testing/profile/profile.py

@@ -30,10 +30,11 @@ def fromFile(f):
                 ret = None
                 with open(f, 'rb') as fd:
                     if impl is lnt.testing.profile.perf.LinuxPerfProfile:
-                        ret = impl.deserialize(fd,
-                                  nm = os.getenv('CMAKE_NM', 'nm'),
-                                  objdump = os.getenv('CMAKE_OBJDUMP', 'objdump'),
-                                  binaryCacheRoot = os.getenv('LNT_BINARY_CACHE_ROOT', ''))
+                        ret = impl.deserialize(
+                            fd,
+                            nm=os.getenv('CMAKE_NM', 'nm'),
+                            objdump=os.getenv('CMAKE_OBJDUMP', 'objdump'),
+                            binaryCacheRoot=os.getenv('LNT_BINARY_CACHE_ROOT', ''))
                     else:
                         ret = impl.deserialize(fd)
                 if ret: