Python 3 - Don't use unbuffered I/O in text mode.

This is unsupported in Python 3.  This could also have been fixed
by using "wb" instead of "w", but it doesn't seem like writing the
session log absolutely *needs* to be unbuffered.

llvm-svn: 252381
diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index 9d0c4e2..e52c5bf 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -1413,8 +1413,8 @@
         self.log_basename = self.getLogBasenameForCurrentTest()
 
         session_file = "{}.log".format(self.log_basename)
-        unbuffered = 0 # 0 is the constant for unbuffered
-        self.session = open(session_file, "w", unbuffered)
+        # Python 3 doesn't support unbuffered I/O in text mode.  Open buffered.
+        self.session = open(session_file, "w")
 
         # Optimistically set __errored__, __failed__, __expected__ to False
         # initially.  If the test errored/failed, the session info