More cleanup on the lldb-perf code:

- TestCase.m_thread is now filled in with the first thread that has a valid
  stop reason. This eliminates the need for the SelectMyThread() functions.
- The first thread that stops for a reason is also set as the selected thread
  in the process in case any command line commands are run.
- Changed launch over to take a SBLaunchInfo parameter so that the launch
  function doesn't keep getting new arguments as they are needed.
- TestCase::Setup() and TestCase::Launch(SBLaunchInfo) now return bool to 
  indicate success of setup and launch.
- ActionWanted::Next(SBThread) was renamed to ActionWanted::StepOver(SBThread)
- ActionWanted::Finish(SBThread) was renamed to ActionWanted::StepOut(SBThread)

llvm-svn: 177376