Refactor initialization in tools for OPENDJ-2616 Support protection of pluggable backend data at rest

Tools have to be able to access cryptographic keys to access and generate backend data.
Keys are stored in the admin backend and ads-truststore, managed themselves as backends, so they must be started for tools to work.
Moreover, each tool had its own server initialization (init) code, so some refactoring was done at that level.
Initialization happens through a DirectoryServer initialization builder, so
that tools can decide which services they need to run.
ImportLDIF, ExportLDIF, RebuildIndex, VerifyIndex, EncodePassword and BackendStat need to access data, so their init was extended to do it.
BackupDB, RestoreDB and ListBackends only init the first part.