Move some portions of test/io to test/modules/standard/FileSystem (part 8 of 11)

This commit moves io/fsouza/isdir and io/fsouza/isfile.  I decided to do those
together, so the number of expected commits is now 11.
Move some portions of test/io to test/modules/standard/FileSystem (part 9 of 11)

This commit moves test/io/fsouza/chown/
Move some portions of test/io to test/modules/standard/FileSystem (part 10 of 10)

This commit moves io/fsouza/chdir and io/fsouza/cwd.  I decided to move these
two together, so this is the last expected commit.