Add additional checks for attributes

Some decorators (like dtt) do have a func attribute
but no "attr" and "value" attribute defined.
This leads to errors during pep8 gate check (see [1]).

[1]: https://review.openstack.org/#/c/153234/4

Closes-Bug: #1431267
Change-Id: Id16bce40e30ecb6bc5bff9b55650acc538ece3a9
1 file changed