Do a second key cleanup in pthread_exit.

During pthread_exit, the keys are cleaned. Unfortunately, a call to
free occurs after the cleanup and the memory for some of the keys
is recreated when using jemalloc. The solution is to do the key
cleanup twice.

Also, modify the pthread_detach__leak test to be less flaky
when run on a jemalloc system.

Bug: 16513133
Change-Id: Ic17e8344bdc1ba053c4f5b6d827a4c19c57860c1