* 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 iosxr modules to support persistent socket
* adds iosxr action plugin to connect to device
* adds exec_command() to iosxr shared module
* fixes iosxr_config and iosxr_template local action
* update all unit test cases
* adds base test module for iosxr module testing
