dev image: change python detection

Older Python versions would force /usr/bin/python creation, but newer
ones do not.  Change the logic from detecting python itself to whether
the wrappers are available.

BUG=b:187795220
TEST=CQ passes

Change-Id: I03be3b2bcc1465c28cf5aeea28c70dfcc45fd5cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3588984
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Cindy Lin <xcl@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
1 file changed