releasetools: Replace key values in permission files during re-signing

Permission files may grant permissions based on signatures in the same
way mac_permissions grants selinux permissions. In order to have this
work properly with dev-key and production key signed builds, allow these
files to be re-written during the signing process to replace the value
of the keys in production signed builds.

Change-Id: Id0311e49f8bba5a9f71b2fa49b480cb74779c853
Ticket: CYNGNOS-1877, RM-179