Bump up the BBOTA version to 4.

To accommodate new changes (such as error correction in [1]) to BBOTA
in N release. We bump up the version to keep the OTA script backward
compatible.

Needs the matching CL in commit
1fdec8685af858c5ff4f45d2e3059186ab5ed2ab.

[1]: commit 0a7b47397db3648afe6f3aeb2abb175934c2cbca

Change-Id: Ib9158b455cd5905fe2d4742ce81feb1b7583054f