Include name of test in filesystem-test.XXXXXX filenames

Include name of test in filesystem-test.XXXXXX filenames

Also fix some tests that were not cleaning up after themselves, as
identified by the change to nonexistent_path.

	* testsuite/util/testsuite_fs.h (nonexistent_path): Include name
	of the source file containing the caller.
	* testsuite/27_io/filesystem/iterators/directory_iterator.cc: Remove
	directories created by test.
	* testsuite/27_io/filesystem/iterators/recursive_directory_iterator.cc:
	Likewise.
	* testsuite/experimental/filesystem/iterators/directory_iterator.cc:
	Likewise.
	* testsuite/experimental/filesystem/iterators/
	recursive_directory_iterator.cc: Likewise.

From-SVN: r267801