Moving unix-only tmp functions into a single block
Re-enable disabled tmp tests

Appears to have been disabled since
02a6aaba79a379228805c76fb62e3b99496e6b23, or, for about two years.
Variable renaming to resolve conflicts with newer code.
f(::Function) variants for `mktemp` and `mktempdir`
Merge pull request #9017 from ninjin/nin/mktmp_do

RFC: f(::Function) variants for `mktemp` and `mktempdir`