Polish up the pipe tests and make them more deterministic

- Make tests requiring "usleep" more deterministic by synchronizing
  message passing using an additional set of pipe file descriptors.
  This fixes determinism issues seen when executing the
  pipe-fstatbug testcase via long kyua runs
- Apply style(9) and WARNS fixes
- Bump WARNS up to 6

Sponsored-by: EMC / Isilon Storage Division
Add an atf_tc_expect_fail for FreeBSD/i386

Sponsored-by: EMC / Isilon Storage Division
Merge branch 'isilon-atf' of https://github.com/yaneurabeya/freebsd into isilon-atf