VPP-1508: Tests: Fix vpp_api struct.error under py3.

Fix struct.error: expected bytes object got <class 'str'>

Change-Id: I837ae6e97e44c789a9372677151b157956525334
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/test_memif.py b/test/test_memif.py
index 6da8bf5..1f98e3f 100644
--- a/test/test_memif.py
+++ b/test/test_memif.py
@@ -3,6 +3,7 @@
 
 from scapy.layers.l2 import Ether
 from scapy.layers.inet import IP, ICMP
+import six
 
 from framework import VppTestCase, VppTestRunner, running_extended_tests
 from remote_test import RemoteClass, RemoteVppTestCase
@@ -45,7 +46,7 @@
     def _check_socket_filename(self, dump, socket_id, filename):
         for d in dump:
             if (d.socket_id == socket_id) and (
-                    d.socket_filename.rstrip("\0") == filename):
+                    d.socket_filename.rstrip(b"\0") == filename):
                 return True
         return False
 
@@ -56,26 +57,28 @@
         dump = self.vapi.memif_socket_filename_dump()
         self.assertTrue(
             self._check_socket_filename(
-                dump, 0, self.tempdir + "/memif.sock"))
+                dump, 0, b"%s/memif.sock" % six.ensure_binary(
+                    self.tempdir, encoding='utf-8')))
 
         memif_sockets = []
         # existing path
         memif_sockets.append(
             VppSocketFilename(
-                self, 1, self.tempdir + "/memif1.sock"))
+                self, 1, b"%s/memif1.sock" % six.ensure_binary(
+                    self.tempdir, encoding='utf-8')))
         # default path (test tempdir)
         memif_sockets.append(
             VppSocketFilename(
                 self,
                 2,
-                "memif2.sock",
+                b"memif2.sock",
                 add_default_folder=True))
         # create new folder in default folder
         memif_sockets.append(
             VppSocketFilename(
                 self,
                 3,
-                "sock/memif3.sock",
+                b"sock/memif3.sock",
                 add_default_folder=True))
 
         for sock in memif_sockets:
@@ -93,7 +96,8 @@
         dump = self.vapi.memif_socket_filename_dump()
         self.assertTrue(
             self._check_socket_filename(
-                dump, 0, self.tempdir + "/memif.sock"))
+                dump, 0, b"%s/memif.sock" % six.ensure_binary(
+                    self.tempdir, encoding='utf-8')))
 
     def _create_delete_test_one_interface(self, memif):
         memif.add_vpp_config()
@@ -146,26 +150,27 @@
         self._create_delete_test_one_interface(memif)
 
     def test_memif_create_custom_socket(self):
-        """ Memif create with non-default socket filname """
+        """ Memif create with non-default socket filename """
 
         memif_sockets = []
         # existing path
         memif_sockets.append(
             VppSocketFilename(
-                self, 1, self.tempdir + "/memif1.sock"))
+                self, 1, b"%s/memif1.sock" % six.ensure_binary(
+                    self.tempdir, encoding='utf-8')))
         # default path (test tempdir)
         memif_sockets.append(
             VppSocketFilename(
                 self,
                 2,
-                "memif2.sock",
+                b"memif2.sock",
                 add_default_folder=True))
         # create new folder in default folder
         memif_sockets.append(
             VppSocketFilename(
                 self,
                 3,
-                "sock/memif3.sock",
+                b"sock/memif3.sock",
                 add_default_folder=True))
 
         memif = VppMemif(self, MEMIF_ROLE.SLAVE, MEMIF_MODE.ETHERNET)
@@ -184,7 +189,8 @@
                          ring_size=1024, buffer_size=2048)
 
         remote_socket = VppSocketFilename(self.remote_test, 1,
-                                          self.tempdir + "/memif.sock")
+                                          b"%s/memif.sock" % six.ensure_binary(
+                                              self.tempdir, encoding='utf-8'))
         remote_socket.add_vpp_config()
 
         remote_memif = VppMemif(self.remote_test, MEMIF_ROLE.MASTER,
@@ -222,7 +228,8 @@
         memif = VppMemif(self, MEMIF_ROLE.SLAVE,  MEMIF_MODE.ETHERNET)
 
         remote_socket = VppSocketFilename(self.remote_test, 1,
-                                          self.tempdir + "/memif.sock")
+                                          b"%s/memif.sock" % six.ensure_binary(
+                                              self.tempdir, encoding='utf-8'))
         remote_socket.add_vpp_config()
 
         remote_memif = VppMemif(self.remote_test, MEMIF_ROLE.MASTER,