Run the tests in a temp directory so we can easily clean up on completion.

Signed-off-by: Shawn Laffan <shawnlaffan@gmail.com>
Get the canary file name from a sub (PAR::get_canary_file_name) rather than hard coding it.

Signed-off-by: Shawn Laffan <shawnlaffan@gmail.com>
PAR.pm: Add a sub PAR::get_canary_file_name to access the canary file name, and create it in a temp dir so it is automatically cleaned up.

21-pp_reinstate_cached_files.t:  Add the PAR/lib folder in a begin block.  Still need to add it only if it exists, and possibly only when in dev testing mode.

Signed-off-by: Shawn Laffan <shawnlaffan@gmail.com>