Migrate CheckAVDevices.py to Python 3

Note: The script does not currently run successfully in master.

BUG=chromium:1031760
TEST=None

Change-Id: Id588b86215ea83229e2af48040dda4685a785140
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1959075
Tested-by: Greg Edelston <gredelston@google.com>
Reviewed-by: Aashutosh Kalyankar <aashutoshk@chromium.org>
Commit-Queue: Greg Edelston <gredelston@google.com>
diff --git a/provingground/av_analysis/CheckAVDevices.py b/provingground/av_analysis/CheckAVDevices.py
index d389a56..204e453 100755
--- a/provingground/av_analysis/CheckAVDevices.py
+++ b/provingground/av_analysis/CheckAVDevices.py
@@ -1,6 +1,5 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
-from __future__ import unicode_literals
 import json
 import os
 import sys
@@ -66,7 +65,7 @@
     rec_name = host + _recorder + _cros
     rec_ping_args = ['ping', '-c', '1', rec_name]
     response = subprocess.call(rec_ping_args, stdout=_FNULL)
-    print "REC: {0:50} Ping Result: {1}".format(rec_name, response)
+    print("REC: {0:50} Ping Result: {1}".format(rec_name, response))
 
 
 def update_servlet(host):