tests: move some files to the tests package

some test support libraries had escaped confinement and were found
wandering around the utilities package:

/usr/tests/lib/csu/dynamiclib/libh_csu.so
/usr/tests/lib/libthr/dlopen/h_pthread_dlopen.so
/usr/tests/lib/libthr/dlopen/h_pthread_dlopen.so.1
/usr/tests/sys/vm/stack/libsoxstack.so

these aren't built using bsd.test.mk, so they don't get the default
PACKAGE=tests option; set this by hand in their Makefiles to put them
back where they belong.

Reviewed by: manu, des, emaste
Approved by: des (mentor)
Differential Revision: https://reviews.freebsd.org/D50147