Merge changes from topic "snapshot_fuzz"

* changes:
  libsnapshot_fuzzer: Add tests
  libsnapshot_fuzzer: add initial corpus
  libsnapshot_fuzzer: Attempt to cleanup env before and after
  libsnapshot_fuzzer: add new test directive to switch slot
  libsnapshot_fuzzer: mount data image
  libsnapshot_fuzzer: also create snapshots dir
  libsnapshot_fuzzer: Add ZERO to operation types