Format log_begin_time timestamp for output file names in cat_adb_log.

Bug: None
Test: locally with act.py
Change-Id: Ibe11001dceb42c1f19fabba9dd68baaa8986e51e
diff --git a/acts/framework/acts/controllers/android_device.py b/acts/framework/acts/controllers/android_device.py
index 84709aa..a774de4 100755
--- a/acts/framework/acts/controllers/android_device.py
+++ b/acts/framework/acts/controllers/android_device.py
@@ -722,7 +722,9 @@
             return
         adb_excerpt_dir = os.path.join(self.log_path, dest_path)
         utils.create_dir(adb_excerpt_dir)
-        out_name = '%s,%s.txt' % (log_begin_time, self.serial)
+        out_name = '%s,%s.txt' % (
+            acts_logger.normalize_log_line_timestamp(log_begin_time),
+            self.serial)
         tag_len = utils.MAX_FILENAME_LEN - len(out_name)
         out_name = '%s,%s' % (tag[:tag_len], out_name)
         adb_excerpt_path = os.path.join(adb_excerpt_dir, out_name)