Modifies the log directory to ensure that the log file will be found on tear-down (i.e. for CI agents that clean up artifacts aggressively).

- Uses the cwd following the model of TestPublicAPIHeaders.py


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@182116 91177308-0d34-0410-b5e6-96231b3b80d8