mnesia_rocksdb/test

To run the mnesia test suite, replacing disc_only_copies references with
rocksdb_copies:

```
cd $ERL_TOP
make release_tests
cd release/tests/mnesia_test
cp $MNESIA_ROCKSDB/test/mnesia_rocksdb_backend_xform.erl .
cp $MNESIA_ROCKSDB/test/Emakefile .
```

You may use github.com/uwiger/parse_trans, and pretty-print the
debug_info in the transformed test suite modules using the following alias:

```
alias pp='escript $PARSE_TRANS_ROOT/ebin/parse_trans_pp.beam'
```