Upgrade Apache DS to version AM26

Currently, we are using version M24. This version included a dependency to ehCache, which is used in the classes to create in-memory ApacheDS DirectoryServices for various LDAP tests. 

Version AM26 no longer uses ehCache, and uses Caffeine Cache instead, so upgrading to this version would involve updating InMemoryDirectoryServiceFactory and InMemorySchemaPartition to make use of Caffeine Cache instead.

Known issues when upgrading to AM26 include: 

• ApacheDS expects the KeyStore to only contain a single entry, it may be sufficient to remove the CA certificate from the KeyStore.
• Base search DNs need to include the organizational unit, or we could get some LdapReferralExceptions with unprocessed continuation references.