Add messages to inform users that reproxy is shutting down

Otherwise there can be a moment at the end of the build where it feels like ninja hangs when you ctrl-c to kill

Bug: b/264405266
Change-Id: Ie67b48cb3ceb624885dc4cf62d5bd631a763ee76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4286582
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Ben Segall <bentekkie@google.com>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>

ninja_reclient.py

@@ -136,9 +136,11 @@ def main(argv):
   try:
     return ninja.main(argv)
   except KeyboardInterrupt:
+    print("Caught User Interrupt", file=sys.stderr)
     # Suppress python stack trace if ninja is interrupted
     return 1
   finally:
+    print("Shutting down reproxy...", file=sys.stderr)
     stop_reproxy(reclient_cfg, reclient_bin_dir)