1. Implemented SSHAuth
2. Old initialization API has been marked as deprecated
3. SFTP is started on demand with 3 retries
4. Reworked unit test to cover 100%
5. Added docstrings
6. Remove cyclic SSH session initialization in helper
7. Code is ready for adopted memorize pattern
blueprint: sshmanager-integration
Change-Id: I49d0aa635ba3f3125ab17531c0790a0106b87fea