BUG: Index.name is lost during timedelta ops
Closes #9926.

CC @hsperr I've changed `common._maybe_match_names` to work with not-named objects, and hopefully can use in #9965 also.

while refactoring my code from #9965 to use this I found that it might be nice to have the same method for multiindex with the 'names' attribute instead, what do you think?
 It is nice the same logic can be used. please change it accordingly on your pr, and I'll rebase.
 thanks @sinhrks 
