tools: Add tool for listing outdated pip packages.

tools/list-outdated-packages

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+import subprocess
+import os
+
+ZULIP_PATH = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+os.chdir(ZULIP_PATH)
+
+output = subprocess.check_output(['pip', 'list', '--outdated', '--format',
+                                  'columns']).decode('utf-8').splitlines()
+
+packages_info = output[2:]
+
+for package_line in packages_info:
+    package_name = package_line.split()[0]
+    package_current_version = package_line.split()[1]
+    package_latest_version = package_line.split()[2]
+    try:
+        output = subprocess.check_output(['grep', '-r', package_name, 'requirements', '--exclude=*.txt',
+                                          '--include=pip.txt']).decode('utf-8')
+        print(package_name, "|", package_current_version, "|", package_latest_version)
+    except subprocess.CalledProcessError:
+        pass