Stop sending terminal escape sequences if we're redirecting output to a file.

tools/run_tests/jobset.py

@@ -101,6 +101,7 @@ def message(tag, msg, explanatory_text=None, do_newline=False):
     print '%s: %s' % (tag, msg)
     return
   try:
+    if sys.stdout.isatty():
         sys.stdout.write('%s%s%s\x1b[%d;%dm%s\x1b[0m: %s%s' % (
             _BEGINNING_OF_LINE,
             _CLEAR_LINE,
@@ -110,6 +111,12 @@ def message(tag, msg, explanatory_text=None, do_newline=False):
             tag,
             msg,
             '\n' if do_newline or explanatory_text is not None else ''))
+    else:
+        sys.stdout.write('%s%s: %s%s' % (
+            '\n%s' % explanatory_text if explanatory_text is not None else '',
+            tag,
+            msg,
+            '\n'))
     sys.stdout.flush()
   except:
     pass