The previous pthread_key_create_many test was really
pthread_key_create_all, which has proven very difficult to test
correctly (because it is affected by any other parts of the system using
pthread keys, and that can vary with test ordering). It also tested
expected values of PTHREAD_KEYS_MAX and the associated sysconf() value,
rather than those being in their own test.
Instead, split this test into a few distinct tests:
* pthread.pthread_keys_max
* pthread._SC_THREAD_KEYS_MAX_big_enough_for_POSIX
* pthread.pthread_key_many_distinct
* We actually didn't have a test to ensure that the keys we were
creating were distinct.
* pthread.pthread_key_EAGAIN
* Make sure pthread_key_create() will _eventually_ fail with
EAGAIN, not at a (sometimes incorrectly) predetermined maximum.
Change-Id: Iff1e4fdcc02404094bde0418122c64c227cf1702