Test framework: StringIO fixes for Python3

Add 2/3 support to binarytomac and mactobinary and move to vpp_mac.py

Change-Id: I3dc7e4a24486aee22140c781aae7e44e58935877
Signed-off-by: Ole Troan <ot@cisco.com>
diff --git a/src/vpp-api/python/vpp_papi/vpp_stats.py b/src/vpp-api/python/vpp_papi/vpp_stats.py
index bb6cdf5..06daaf8 100644
--- a/src/vpp-api/python/vpp_papi/vpp_stats.py
+++ b/src/vpp-api/python/vpp_papi/vpp_stats.py
@@ -196,8 +196,13 @@
         retries = 0
         while True:
             try:
-                dir = self.ls(name)
-                return self.dump(dir).values()[0]
+                d = self.ls(name)
+                s = self.dump(d)
+                if len(s) > 1:
+                    raise AttributeError('Matches multiple counters {}'
+                                         .format(name))
+                k, v = s.popitem()
+                return v
             except VPPStatsIOError as e:
                 if retries > 10:
                     return None