Update ota script to match init's logic

In aosp/1459042, init has updated it's logic to use
ro.build.version.release_or_codename for fingerprint calculation.
The ota script needs the same update for ota targeting to work
correctly.

As a best effort to support pre-S dev stage builds, use
ro.build.version.release for sdk version < 30.

Bug: 170968068
Bug: 158483506
Test: unit tests, generate an OTA for S build
Change-Id: I01ca8a3b7b8b58f94b10f90ed0d27e688a72b866