gs: rm: add -- before path

This shouldn't normally be an issue, but we're defensive in other
gs subcommands, so should be defensive here too.

BUG=None
TEST=CQ passes

Change-Id: I7f07b453534581cff5759742073e0f66aca4d13f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2386035
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/gs.py b/lib/gs.py
index 548de2d..c63b4ae 100644
--- a/lib/gs.py
+++ b/lib/gs.py
@@ -1176,6 +1176,7 @@
       raise TypeError('"recurse" has been renamed to "recursive"')
     if recursive:
       cmd.append('-R')
+    cmd.append('--')
     cmd.append(path)
     try:
       self.DoCommand(cmd, **kwargs)
diff --git a/lib/gs_unittest.py b/lib/gs_unittest.py
index 73867f4..db323b0 100644
--- a/lib/gs_unittest.py
+++ b/lib/gs_unittest.py
@@ -631,7 +631,7 @@
 
   def testMissing(self):
     """Test behavior w/missing files."""
-    self.gs_mock.AddCmdResult(['rm', 'gs://foo/bar'],
+    self.gs_mock.AddCmdResult(['rm', '--', 'gs://foo/bar'],
                               error='CommandException: No URLs matched: '
                                     'gs://foo/bar',
                               returncode=1)