rose suite-clean --only=GLOBS

New `--only=GLOBS` option to restrict items to be cleaned.
Improve diagnostic.

rose test battery: use number of processors as number of jobs.

I'll mark this as a change to close #914, as I believe this change handles its main use case.
It is not too bad if you think of it as "don't clean everything, but only `share` and `work`". Other good alternatives would be `--item=` or `--glob=`, but I have settled on `--only=` mainly because it implies more strongly the "don't clean everything" logic.