Code refactoring (#889)

* Add __all__ to all module and plugin utils.

* Convert quite a few positional args to keyword args.

* Avoid Python 3.8+ syntax.

plugins/module_utils/_crypto/_obj2txt.py

@@ -58,3 +58,6 @@ def obj2txt(openssl_lib, openssl_ffi, obj) -> str:
         buf = openssl_ffi.new("char[]", buf_len)
         res = openssl_lib.OBJ_obj2txt(buf, buf_len, obj, 1)
     return openssl_ffi.buffer(buf, res)[:].decode()
+
+
+__all__ = ("obj2txt",)