ENH/TST: Allow more keywords to ensure_clean
These keywords will be passed through to `tempfile` constructor functions.

Follow-up:

https://github.com/pandas-dev/pandas/pull/30771#discussion_r363684666
@WillAyd @jreback : Any further thoughts on this? I would still vote for explicit arguments if anything but certainly open to input of others @pandas-dev/pandas-core : Thoughts?  There seems to be some impasse regarding whether we should surface explicit arguments.  I'm all for being explicit, but I also want them to make sense for both `mkstemp` and `TemporaryFile` and not just one.

As we have it, `filename` is used consistently for both constructor functions. this is fine as its only for testing, thanks @gfyoung 

however, I think it would be interesting to separate ensure_clean to 2 functions, e.g. ensure_clean_dir and ensure_clean_file; then you *could* have named keywords.

not sure how much work that would be but might be a good followup .