Integrate code from tools/regression into ATF/Kyua

The pull request integrates pieces that EMC Isilon integrated into the build/Kyua.

This was done in a "clean room" manner.

- tools/regression/lib/msun was merged in to lib/msun/tests/legacy to avoid collisions with the NetBSD testcases already present in lib/msun/tests .
- tools/regression/lib/* was merged in to their respective places in the source tree, e.g. tools/regression/lib/libnv -> lib/libnv/tests .
- The failing t_exp testcases were marked atf_tc_expect_fail because of the epsilon error margin that was being tested against was violated.
- tests/sys/execve/good_script was changed to use /bin/sh instead of /bin/csh as /bin/csh is optional with ${MK_TCSH} == whereas /bin/sh is more of a hard requirement.
- Remove Isilon modifications to BSD.tests.dist so BSD.tests.dist is untainted.