* move set_module_args to units.modules.utils
* unit tests: reuse set_module_args
* unit tests: mock exit/fail_json in module.utils.ModuleTestCase
* unit tests: use module.utils.ModuleTestCase
* unit tests: fix 'import shadowed by loop variable'
* updates all vyos modules to use socket connection
* adds vyos local action handler
* adds exec_command() to vyos
* updates vyos_config local action
* update unit test cases
* add base class for testing vyos modules
