Move dict_merge from azure_rm_resource module to
module_utils.common.dict_transformations and add tests.
Use dict_merge to provide a fairly realistic, reliable
diff output when k8s-based modules are run in check_mode.
Rename unit tests so that they actually run and reflect
the module_utils they're based on.
Since it will be used outside just AWS modules, this commit moves
`camel_dict_to_snake_dict` and `snake_dict_to_camel_dict` functions into
a new module_utils file under common/ to match their wider usage.
Matt Clay
Will Thames
Ryan Brown