Changes included:
- non standard docker image (alpine-postgres)
- new setting in vagrant-settings.yaml_defaults (solar_db_backend)
- multidb logic in playbooks (databases.yaml)
- possibility to set backend by SOLAR_DB_BACKEND in jenkins run.sh
- packer images version 0.3.0.pre0 (pre builded docker image)
Change-Id: Id48236aa778597ed787f8455ec4d4c869d0ef1cf
Closes-bug: #1546205