[Python: flake8] Update the utils/python_lint.py script to fail with a non-zero exit code if flake8 and flake8-import-order are not installed.

(cherry picked from commit c096e29)

Author: Ross Bayer

utils/gyb.py

@@ -1133,16 +1133,6 @@ def execute_template(
 
 
 def main():
-    """
-    Lint this file.
-    >>> import sys
-    >>> gyb_path = os.path.realpath(__file__).replace('.pyc', '.py')
-    >>> sys.path.append(os.path.dirname(gyb_path))
-    >>> import python_lint
-    >>> python_lint.lint([gyb_path], verbose=False)
-    0
-    """
-
     import argparse
     import sys
 

utils/line-directive

@@ -659,10 +659,6 @@ def run():
     >>> raw_output.close()
     >>> os.remove(raw_output.name)
 
-    Lint this file.
-    >>> import python_lint
-    >>> python_lint.lint([os.path.realpath(__file__)], verbose=False)
-    0
     """
     if len(sys.argv) <= 1:
         import doctest

utils/python_lint.py

@@ -84,7 +84,7 @@ def lint(args, verbose=False):
         if verbose:
             print(_INSTALL_FLAKE8_MESSAGE)
 
-        return 0
+        return 1
 
     return subprocess.call(
         [sys.executable, '-m', 'flake8'] + args,

validation-test/Python/python-lint.swift

@@ -0,0 +1,8 @@
+// Continuous integration for the OS X Platform also runs the tests in the
+// iPhone, Apple TV and Apple Watch simulators. We only need to run the
+// Python lint once per OSX Platform test run, rather than once for each
+// supported Apple device.
+
+// REQUIRES: OS=macosx
+
+// RUN: %{python} %utils/python_lint.py