Add shebang to servlet.py

Per go/cros-python3-howto, this is the shebang that should be kept
compatible with both Python2 and Python3. Autotest is fragile, so I'm
playing it safe here.

BUG=chromium:1031760
TEST=Run servlet.py in both python2 and python3, and run lib2to3 on
servlet.py

Change-Id: Ia5125bbd075defe69e20523faf36ea58be784c2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1959080
Tested-by: Greg Edelston <gredelston@google.com>
Reviewed-by: Max Timkovich <timkovich@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Greg Edelston <gredelston@google.com>
1 file changed