Spark Accumulo library Kerberos support

[GCHQDeveloper314]

Kerberos support will be added to the Accumulo store under #2614. This doesn't include adding support for Kerberos to the Spark Accumulo library. Adding that support will build on the work done under #2614.

In addition to code changes in the Spark Accumulo library module, this will also require changes to the Accumulo store to refactor methods (especially those related to updateConfiguration()) which support the Spark Accumulo library.

Some of the methods which require changes use internal Accumulo API, therefore it might not be possible to start this until #2664 has been completed, depending on the versions of Accumulo which need to be supported at the time.