AccumuloVFSClassloader creates conflicting local cache directory names when vfs.cache.dir property is set.

When the vfs.cache.dir property is not set, the AccumuloVFSClassloader will use java.io.tmpdir as a base directory for the local cache of jars and then generate a unique directory name using a combination of the processid, hostname and userid executing the JVM.

When the vfs.cache.dir property is set, that value is used as the base directory and an attempt to generate a unique directory is made using an AtomicInteger. This isn't suitable because for non-long lived processes, this will always be 1 - and there's a good chance that directory already exists and is owned by another user, and not writable to by the user in question.

This leads to a failure of the invoked accumulo component to start.

Modify the behavior of the unique directory creation when vfs.cache.dir is set so that it employs the same mechanism for unique directory naming that is used when it is not set.