auto-t: timestamp log files in test-runner

The log files become much more useful when there are timestamps
associated with each log.

tools/utils.py

@@ -6,6 +6,7 @@ import traceback
 import shutil
 import dbus
 
+from datetime import datetime
 from gi.repository import GLib
 from weakref import WeakValueDictionary
 from re import fullmatch
@@ -125,7 +126,11 @@ class Process(subprocess.Popen):
 	@staticmethod
 	def _write_io(instance, data, stdout=True):
 		for f in instance.write_fds:
-			f.write(data)
+			for c in data:
+				f.write(c)
+				if c == '\n':
+					stamp = datetime.strftime(datetime.now(), "%Y-%m-%d %H:%M:%S.%f")
+					f.write(stamp + ': ')
 
 			# Write out a separator so multiple process calls per
 			# test are easer to read.