check_ota_package_signature.py: Set up PYTHONPATH.

... to include system/update_engine/scripts if ANDROID_BUILD_TOP is set
(e.g. after lunching a target).

Test: ./build/make/tools/releasetools/check_ota_package_signature.py
      works without manually setting PYTHONPATH.
Change-Id: I0c5101fab2dd69cb6a598b909aa04bc4d5f45284
1 file changed