Revert^2 "Determine build_ota_package based on recovery.fstab install location"

This change resubmits https://r.android.com/3461419.

recovery_fstab can be installed even if is not defined via
TARGET_RECOVERY_FSTAB_GENRULE. This change modifies the conditional in
determining build_ota_package to take such scenarios into account.

Test: m otapackage
Change-Id: Id4cdd1b0d9953535cee9096047e432bcf8a0fa10