testHostCommands: accept both ethX and en.*X interfaces

systemd (Ubuntu 16) names interfaces like this:
enp1s3 for "ethernet, PCI bus 1, slot 3"

We now accept both in testHostCommands

Fixes #665

mininet/test/test_walkthrough.py

@@ -91,7 +91,8 @@ class testWalkthrough( unittest.TestCase ):
         "Test ifconfig and ps on h1 and s1"
         p = pexpect.spawn( 'mn' )
         p.expect( self.prompt )
-        interfaces = [ 'h1-eth0', 's1-eth1', '[^-]eth0', 'lo', self.prompt ]
+        # Third pattern is a local interface beginning with 'eth' or 'en'
+        interfaces = [ 'h1-eth0', 's1-eth1', '[^-](eth|en)\w*\d', 'lo', self.prompt ]
         # h1 ifconfig
         p.sendline( 'h1 ifconfig -a' )
         ifcount = 0
@@ -117,7 +118,7 @@ class testWalkthrough( unittest.TestCase ):
                 ifcount += 1
             else:
                 break
-        self.assertEqual( ifcount, 3, 'Missing interfaces on s1')
+        self.assertTrue( ifcount >= 3, 'Missing interfaces on s1')
         # h1 ps
         p.sendline( "h1 ps -a | egrep -v 'ps|grep'" )
         p.expect( self.prompt )