find.t: Use temporary testing directory for all blocks of tests.

find.t: Use temporary testing directory for all blocks of tests.

During the execution of ext/File-Find/t/taint.t certain files and directories
are created.  As inferred from smoke-test reports, when testing in parallel
these entities ran the risk of being detected by certain tests in
ext/File-Find/t/find.t, thereby causing intermittent failures in the smoke
tests.

Problem is being addressed by (a) moving the block of tests created in August 2014
(RT #122547) to prevent processing of misspelled options to a place in the
file where we have moved from the current working directory one level down to
a temporary testing directory; and (b) providing a list of basenames of files
we expect to find therewithin.