Check for pthread_create errors and move barrier logic into harness

If thread creation fails then join with existing threads and exit.

Moved the before/after barrier logic into the test harness rather
than the futex_[set]wait_test functions.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Darren Hart <dvhltc@us.ibm.com>