rose bush: cast ws args to str before shlex

It appears that in newer version of cherrypy, query arguments are
encoded in Unicode. Unfortunately, using `shlex.split` on a Unicode
string gives garbage. Casting the arguments into a `str` solves the
problem.
Merge pull request #997 from matthewrmshin/rose-bush-shlex-unicode

rose bush: cast ws args to str before shlex
test-battery: `cylc unregister` where appropriate
Merge pull request #998 from matthewrmshin/t.cylc-unregister

test-battery: `cylc unregister` where appropriate