Make TestThreadStates more stable

Summary:
Because of the large number of XFAILs TestThreadStates has decayed quite a bit. This commit does
the following:
- removes the "breakpoint list" expectations. Most tests have been failing on this, because the
  command output changed quite a while back. I remove it, because run_break_set_by_file_and_line
  already does a decent amount of checking
- fixup test_state_after_expression: this was calling the wrong function by mistake. As now the
  function actually tests something (which we know is broken), I needed to XFAIL it as well.
- replaces the sleep() with a proper wait-for-event functionality in parts which use async mode,
  to stabilize the one function that actually tests something.

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D15233

llvm-svn: 254901