new_variant: scripts detect and warn when standalone

Have the various scripts detect that they are running standalone and
offer the user information about using new_variant.py instead.

BUG=b:162258393
TEST=`./create_coreboot_config.sh volteer volteer gnastygnorc`
and you get a nice warning message about how you could be using
new_variant.py instead.

Change-Id: Ib0908c883338be89f86357a4ea984de1893d0eaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2320893
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
7 files changed