Ceph

In general, we need to make sure that concurrent operation works properly with RADOS / librados / DHO.
We have never used librados in a multi-threaded context before (it wasn't possible before issue #815 was resolved).

This task involves analyzing the code from a high level, and also writing tests of all the various cases. The tests should be integrated with Teuthology to prevent regressions.

The same tests can be used to test librados multi-process concurrency and multi-thread concurrency. You simply have a piece of code that can either do fork() and pthread_create(), and a later one that either does join() or pthread_join().