JanusGraphSimpleAuthenticator (credentialsDb) does not work for Berkeleyje storage backend

In two independent reports, users started configuring the JanusGraphSimpleAuthenticator with a Berkeleyje storage backend and only hit a "invalid username/password" upon remote connection:
[https://lists.lfaidata.foundation/g/janusgraph-users/topic/authentication_in_janusgraph/81052019 ](https://lists.lfaidata.foundation/g/janusgraph-users/topic/authentication_in_janusgraph/81052019 )
[https://groups.google.com/g/janusgraph-users/c/iVqlUS2zQbc/m/vmf8PgEQBAAJ ](https://groups.google.com/g/janusgraph-users/c/iVqlUS2zQbc/m/vmf8PgEQBAAJ )
This failing behavior was encountered on both janusgraph-0.5.3 and janusgraph-0.3.2. Apparently, there is some incompatibility between JanusGraphSimpleAuthenticator and the berkeleyje storage backend. New users added to the credentialsdb are in fact committed to the storage and can be retrieved by opening the credentials graph in the gremlin console, see the links above for more details.

Because the Berkeley is not an important storage backend to JanusGraph, the workaround is simple: choose a different storage backend for the credentialsDb.

Start by reproducing remote authentication with JanusGraphSimpleAuthenticator and a Berkeleyje storage backend, using the credentialsDb setup described in the issue. Inspect the credentials graph in the Gremlin console to compare committed users with authentication lookup behavior. Done means identifying and fixing the incompatibility, or documenting the limitation if Berkeleyje is unsupported.

Written by the indexing model from the issue text.