git_cl: add a long option for git cl patch -b

R=sokcevic

Fixed: 1492418
Change-Id: I09b7b05c8eb4968f079303406c474f90c34b66a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4937884
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>
Auto-Submit: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

git_cl.py

@@ -5500,6 +5500,7 @@ def CMDland(parser, args):
 def CMDpatch(parser, args):
     """Applies (cherry-picks) a Gerrit changelist locally."""
     parser.add_option('-b',
+                      '--branch',
                       dest='newbranch',
                       help='create a new branch off trunk for the patch')
     parser.add_option('-f',