cbuildbot: only check for inside the chroot after parsing args

This allows cbuildbot_unittest to run inside the chroot. Some of the
unit tests only test argument parsing and fail incorrectly without this
change.

BUG=none
TEST=unit tests

Change-Id: I1294d1e498f2a9b598780719eb5d05ce504437d8
Reviewed-on: https://gerrit.chromium.org/gerrit/32027
Tested-by: Zdenek Behan <zbehan@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Commit-Ready: Zdenek Behan <zbehan@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 5b0e8ec..ea49e93 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -1096,14 +1096,15 @@
   # Set umask to 022 so files created by buildbot are readable.
   os.umask(022)
 
-  if cros_build_lib.IsInsideChroot():
-    cros_build_lib.Die('Please run cbuildbot from outside the chroot.')
-
   parser = _CreateParser()
   (options, args) = _ParseCommandLine(parser, argv)
 
   _PostParseCheck(options, args)
 
+  if cros_build_lib.IsInsideChroot():
+    cros_build_lib.Die('Please run cbuildbot from outside the chroot.')
+
+
   if options.remote:
     cros_build_lib.logger.setLevel(logging.WARNING)