Merge changes from topic "snapshot_fuzz"

* changes:
  Enable automatic libsnapshot fuzzer runs
  Also log corpus when aborted through libbase.
  libsnapshot_fuzzer: Fuzz MapUpdateSnapshot.
  libsnapshot_fuzzer: construct valid super partition metadata.
  libsnapshot_fuzzer: Fuzz CreateUpdateSnapshots
  libsnapshot_fuzzer: add additional tests for more APIs
  libsnapshot_fuzzer: use protobuf
  libsnapshot_fuzzer: map super image