Python 3 - Use universal_newlines=True in subprocess.Popen.

This follows the spirit of a previous patch which did essentially
the same thing.  In Python 3, when you use Popen.communicate(),
you get back a bytes object which cannot normally be treated as
a string.  We could decode this manually, but universal_newlines=True
does this automatically, and there's no disadvantage to doing so
even on Python 2.  So just enable it always.

llvm-svn: 252126

lldb/packages/Python/lldbsuite/test/test_runner/lib/process_control.py

@@ -271,6 +271,7 @@ class UnixProcessHelper(ProcessHelper):
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
+            universal_newlines=True, # Elicits automatic byte -> string decoding in Py3
             close_fds=True,
             preexec_fn=preexec_func)
 
@@ -383,6 +384,7 @@ class WindowsProcessHelper(ProcessHelper):
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
+            universal_newlines=True, # Elicits automatic byte -> string decoding in Py3
             creationflags=creation_flags)
 
     def was_hard_terminate(self, returncode):