Revert "gclient: return non-zero exit code on unknown command"

This reverts commit 2c199e1e.

Reason for revert: This makes calls to gclient that have the only intention of updating gclient fail, like:
https://cs.chromium.org/chromium/src/v8/tools/try_perf.py?l=93

Reverting for now to give time to clean up such scripts before reland.

Original change's description:
> gclient: return non-zero exit code on unknown command
> 
> Bug: none
> Change-Id: I447f66765679b7b66b5748af1cf1f501610603bf
> Reviewed-on: https://chromium-review.googlesource.com/504408
> Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
> Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
> 

TBR=iannucci@chromium.org,phajdan.jr@chromium.org,dpranke@chromium.org,tandrii@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Bug: none

Change-Id: I9496f7192dfde1e38c186a94ac985190b76b2438
Reviewed-on: https://chromium-review.googlesource.com/506563Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>

subcommand.py

@@ -66,8 +66,13 @@ def epilog(text):
 
 def CMDhelp(parser, args):
   """Prints list of commands or help for a specific command."""
-  parser.print_help()
-  return 0
+  # This is the default help implementation. It can be disabled or overriden if
+  # wanted.
+  if not any(i in ('-h', '--help') for i in args):
+    args = args + ['--help']
+  _, args = parser.parse_args(args)
+  # Never gets there.
+  assert False
 
 
 def _get_color_module():
@@ -250,9 +255,7 @@ class CommandDispatcher(object):
     if cmdhelp:
       # Not a known command. Default to help.
       self._add_command_usage(parser, cmdhelp)
-      # Make sure we return a non-zero exit code for unknown commands.
-      rc = cmdhelp(parser, args)
-      return rc if rc != 0 else 2
+      return cmdhelp(parser, args)
 
     # Nothing can be done.
     return 2

tests/gclient_smoketest.py

@@ -165,8 +165,7 @@ class GClientSmoke(GClientSmokeBase):
     self.assertTrue(1000 < len(result[0]) and len(result[0]) < 2300,
                     'Too much written to stdout: %d bytes' % len(result[0]))
     self.assertEquals(0, len(result[1]))
-    # An unknown command should result in non-zero exit code.
-    self.assertEquals(2, result[2])
+    self.assertEquals(0, result[2])
 
   def testNotConfigured(self):
     res = ('', 'Error: client not configured; see \'gclient config\'\n', 1)