build_packages: fix inverted cli flag

shflags provides positive/negative variants for all boolean flags
for us automatically.  Declaring the flag as negative up front will
break this as we end up with --nonoworkon.

BUG=None
TEST=CQ passes

Change-Id: Ia638470ff2b1612aefac0bc0624bf3276459afe3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/1913490
Reviewed-by: Craig Hesling <hesling@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Nicolas Boichat <drinkcat@chromium.org>
1 file changed