Update docs and command line flags for MB.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index e7ef57b63efe391f2cb8df238839cd744240b8ee..3a24f6104e1558543f2cd0697eed65cb601abc06 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -65,8 +65,8 @@ class MetaBuildWrapper(object):
                         help='Do a dry run (i.e., do nothing, just print '
                              'the commands that will run)')
       subp.add_argument('-q', '--quiet', action='store_true',
-                        help='Do not print anything, just return an exit '
-                             'code.')
+                        help='Do not print anything on success, '
+                             'just return an exit code.')
       subp.add_argument('-v', '--verbose', action='count',
                         help='verbose logging (may specify multiple times).')
 
@@ -77,9 +77,6 @@ class MetaBuildWrapper(object):
                             help='analyze whether changes to a set of files '
                                  'will cause a set of binaries to be rebuilt.')
     AddCommonOptions(subp)
-    subp.add_argument('--swarming-targets-file',
-                      help='save runtime dependencies for targets listed '
-                           'in file.')
     subp.add_argument('path', nargs=1,
                       help='path build was generated into.')
     subp.add_argument('input_path', nargs=1,
@@ -108,7 +105,13 @@ class MetaBuildWrapper(object):
 
     subp = subps.add_parser('validate',
                             help='validate the config file')
-    AddCommonOptions(subp)
+    subp.add_argument('-f', '--config-file', metavar='PATH',
+                      default=self.default_config,
+                      help='path to config file '
+                          '(default is //tools/mb/mb_config.pyl)')
+    subp.add_argument('-q', '--quiet', action='store_true',
+                      help='Do not print anything on success, '
+                           'just return an exit code.')
     subp.set_defaults(func=self.CmdValidate)
 
     subp = subps.add_parser('help',