Fix hangs when running pylint with py3

R=gavinmak@google.com

Bug: 1280381
Change-Id: I9bec0f371aa300e2418ac1c200683c02b7e66cb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3350910Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

pylint-1.5

@@ -75,4 +75,5 @@ import sys
 
 import pylint_main
 
-sys.exit(pylint_main.main(sys.argv[1:]))
+if __name__ == '__main__':
+  sys.exit(pylint_main.main(sys.argv[1:]))

pylint-2.6

@@ -68,4 +68,5 @@ import sys
 
 import pylint_main
 
-sys.exit(pylint_main.main(sys.argv[1:]))
+if __name__ == '__main__':
+  sys.exit(pylint_main.main(sys.argv[1:]))

pylint-2.7

@@ -68,4 +68,5 @@ import sys
 
 import pylint_main
 
-sys.exit(pylint_main.main(sys.argv[1:]))
+if __name__ == '__main__':
+  sys.exit(pylint_main.main(sys.argv[1:]))