* Fix ansible-doc traceback for removed modules.
This avoids tracebacks with errors like the following when a module has been removed:
module module_name missing documentation (or could not parse documentation): 'NoneType' object does not support item assignment
* Fix ansible-doc sanity test warning handling.
Warnings about removed modules/plugins on stderr are now properly ignored.
Previously an ansible-doc error could result in unrelated errors going undetected because tests were stopped early and the underlying error was ignored.
