MFC r289172,r290254:

r289172:

Refactor the test/ Makefiles after recent changes to bsd.test.mk (r289158) and
netbsd-tests.test.mk (r289151)

- Eliminate explicit OBJTOP/SRCTOP setting
- Convert all ad hoc NetBSD test integration over to netbsd-tests.test.mk
- Remove unnecessary TESTSDIR setting
- Use SRCTOP where possible for clarity

r290254:

Remove unused variable (SRCDIR)

MFC r277358:

r277358 (by ngie):

Integrate contrib/netbsd-tests/bin/expr into the build/kyua as bin/expr/tests

Sponsored by: EMC / Isilon Storage Division

Integrate contrib/netbsd-tests/bin/expr into the build/kyua as bin/expr/tests

MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division