Remove --bootstrap from cros_sdk help.

The --bootstrap flag should only be used by bots and not by developers.
Several developers have tried running cros_sdk --bootstrap because they
misunderstood the help, and this caused slow builds for developers.

Internal flags that aren't intended for developers shouldn't be displayed
to developers.

BUG=chromium-os:33737
TEST=cros_sdk --help

Change-Id: Iaa061a8f92e1724a0d6b494e18742ac978761e2b
Reviewed-on: https://gerrit.chromium.org/gerrit/31014
Tested-by: David James <davidjames@chromium.org>
Reviewed-by: Zdenek Behan <zbehan@chromium.org>
Commit-Ready: David James <davidjames@chromium.org>
diff --git a/scripts/cros_sdk.py b/scripts/cros_sdk.py
index ebff8bb..c67fe39 100644
--- a/scripts/cros_sdk.py
+++ b/scripts/cros_sdk.py
@@ -267,7 +267,6 @@
 Action taken is the following:
 --enter  (default)  .. Installs and enters a chroot
 --download          .. Just download a chroot (enter if combined with --enter)
---bootstrap         .. Builds a chroot from source (enter if --enter)
 --delete            .. Removes a chroot
 """
   sdk_latest_version = GetLatestVersion()
@@ -275,7 +274,7 @@
   # Actions:
   parser.add_option('--bootstrap',
                     action='store_true', dest='bootstrap', default=False,
-                    help=('Build a new SDK chroot from source'))
+                    help=optparse.SUPPRESS_HELP)
   parser.add_option('--delete',
                     action='store_true', dest='delete', default=False,
                     help=('Delete the current SDK chroot'))