Unit tests using docker

[foglcz]

• Research https://www.docker.com/
• Research https://github.com/osixia/docker-openldap
• Create sample docker images, and individual tests with LDAP configuration
  • Simple authentication
  • Groups loading
  • Thumbnail loading
  • Two domains with a two way trust
  • Two domains with a one way trust
• Integrate the tests into Travis CI
• Add the opensource labels to README.md