Re-enable TestMultithreaded.py test on Linux.

I could not get http://llvm.org/bugs/show_bug.cgi?id=16016)
to fail on my end running 10 times in a row.  Re-enabling
the test.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@202446 91177308-0d34-0410-b5e6-96231b3b80d8
Revert Xcode run argument settings that were accidentally checked in.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@202447 91177308-0d34-0410-b5e6-96231b3b80d8