Make threading tests not depend on the currently selected thread
- tests are now anostic to the currently selected thread, as that is a frontend (i.e. driver) decision
- this is in preparation to a fix to POSIXThread::BreakNotify that will be committed shortly

Reviewed by: Matt Kopec



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@191041 91177308-0d34-0410-b5e6-96231b3b80d8