Fix lint errors on ota_utils.py

Pylint reports lot of error on ota_utils.py, because some members of
OPTIONS object aren't defined. This CL moves some definition from
ota_from_target_files.py to ota_utils.py to fix these lint errors.

Test: Make an OTA package
Change-Id: I1e9f255d5919712b13329046c72650dfac184701