Support --debug CLI option to enable debug logging

Change-Id: Ic40399ff08e5e2384e1db2458099c0fb65b9fa55

gerritlab/main.py

@@ -1,3 +1,4 @@
+import logging
 import shutil
 import time
 import os
@@ -313,6 +314,12 @@ def main():
         nargs="?",
         help="The final branch that commits are intended to be merged into.",
     )
+    parser.add_argument(
+        "--debug",
+        action="store_true",
+        default=False,
+        help="Show debugging information (subprocesses, HTTP requests, etc)."
+    )
     parser.add_argument(
         "--merge",
         "-m",
@@ -336,6 +343,9 @@ def main():
     )
     args = parser.parse_args()
 
+    if args.debug:
+        logging.basicConfig(level=logging.DEBUG)
+
     repo = Repo(os.getcwd(), search_parent_directories=True)
     ensure_commitmsg_hook(repo.git_dir)