[test] Disable CommandScriptImmediateOutputFile on Windows

Somehow the path gets messed up. The command looks correct, but the
python path is not.

(lldb) mywrite
E:\build_slave\lldb-x64-windows-ninja\build\tools\lldb\lit\Commands\
  CommandScriptImmediateOutput\Output\
  CommandScriptImmediateOutputFile.test.tmp.read.txt r

No such file or directory:
'E:build_slavelldb-x64-windows-ninjabuildtoolslldblitCommands
  CommandScriptImmediateOutputOutput
  CommandScriptImmediateOutputFile.test.tmp.read.txt'

Maybe the shlex module is escaping it?

llvm-svn: 358213