releasetools: Fix the reference to OPTIONS.info_dict.

sign_target_files_apks.py calls common.GetBootableImage() but without
calling 'OPTIONS = common.OPTIONS' first. In common.GetBootableImage(),
we should use the local info_dict parameter instead of OPTIONS.info_dict.

Test: sign_target_files_apks.py generates signed-TF.zip successfully.

Change-Id: Ia3d32b88691c26e5fb98feea709e3e3c3eb70fdb