Enable validate-config tests and add a new test

[pilou-]

ISSUE TYPE

• Bugfix Pull Request

SUMMARY

validate-config tests:

• enable existing tests
• add a new test

Depends-On: #882

[pilou-]

Pull request rebased (conflict fixed)

[pilou-]

@Voronenko could you review this one ?

Extract from build log (17 passed in 1.91 seconds):

TASK [validate-config : Cat output] ********************************************
task path: /home/travis/build/ansible/ansible-container/test/includes/show-output.yml:3
Using module file /home/travis/virtualenv/python2.7.13/lib/python2.7/site-packages/ansible/modules/commands/command.py
[...]
changed: [localhost] => {
    "changed": true, 
    "cmd": [
        "cat", 
        "./task.output"
    ], 
    "delta": "0:00:00.004054", 
    "end": "2018-06-20 08:12:02.068743", 
    "invocation": {
        "module_args": {
            "_raw_params": "cat \"./task.output\"", 
            "_uses_shell": false, 
            "chdir": null, 
            "creates": null, 
            "executable": null, 
            "removes": null, 
            "stdin": null, 
            "warn": true
        }
    }, 
    "rc": 0, 
    "start": "2018-06-20 08:12:02.064689", 
    "stderr": "", 
    "stderr_lines": [], 
    "stdout": "============================= test session starts ==============================\nplatform linux2 -- Python 2.7.13, pytest-3.2.1, py-1.4.34, pluggy-0.4.0\nrootdir: /home/travis/build/ansible/ansible-container, inifile:\ncollected 17 items\n\n../../test/tests/validate_config.py .................\n\n========================== 17 passed in 1.91 seconds ===========================", 
    "stdout_lines": [
        "============================= test session starts ==============================", 
        "platform linux2 -- Python 2.7.13, pytest-3.2.1, py-1.4.34, pluggy-0.4.0", 
        "rootdir: /home/travis/build/ansible/ansible-container, inifile:", 
        "collected 17 items", 
        "", 
        "../../test/tests/validate_config.py .................", 
        "", 
        "========================== 17 passed in 1.91 seconds ==========================="
    ]

[Voronenko]

@pilou- What issue no PR refers to, if any ?

[pilou-]

@Voronenko this pull-request:

• fix and enable existing validate-config tests
• add a new unit test: test_get_dependencies_for_role

[pilou-]

@gregdek could you merge this one ?