[lit] Ensure test output is converted to strings where possible.

- This cleans up the text output of failing tests when run under PY3.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188416 91177308-0d34-0410-b5e6-96231b3b80d8

utils/lit/lit/util.py

@@ -156,4 +156,14 @@ def executeCommand(command, cwd=None, env=None):
     if exitCode == -signal.SIGINT:
         raise KeyboardInterrupt
 
+    # Ensure the resulting output is always of string type.
+    try:
+        out = str(out.decode('ascii'))
+    except:
+        out = str(out)
+    try:
+        err = str(err.decode('ascii'))
+    except:
+        err = str(err)
+
     return out, err, exitCode