prefix test directory Makefile targets

Since the */test/Makefile.check files are all directly included
in the toplevel Makefile.main, they can't (usefully) contain
generic targets like "check" or "clean", without any namespace
prefix, as the definitions in each Makefile.check will collide.

This adds namespace prefixing to each generic make target in
each sublevel Makefile.check file.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>