Fix test suite

+ Install VPCS and dynamips from GNS3 PPA
 + Drop netifaces-py3 from requirements.txt
 + Fix/update tests to use installed VPCS and dynamips

tests/iou/test_iou_device.py

@@ -8,12 +8,14 @@ def iou(request):
 
     cwd = os.path.dirname(os.path.abspath(__file__))
     iou_path = os.path.join(cwd, "i86bi_linux-ipbase-ms-12.4.bin")
-    iou_device = IOUDevice(iou_path, "/tmp")
+    iou_device = IOUDevice("IOU1", iou_path, "/tmp")
     iou_device.start()
     request.addfinalizer(iou_device.delete)
     return iou_device
 
 
+@pytest.mark.skipif(os.environ["TRAVIS"] == "TRUE",
+                    reason="IOU Image not available on Travis")
 def test_iou_is_started(iou):
 
     print(iou.command())
@@ -21,6 +23,8 @@ def test_iou_is_started(iou):
     assert iou.is_running()
 
 
+@pytest.mark.skipif(os.environ["TRAVIS"] == "TRUE",
+                    reason="IOU Image not available on Travis")
 def test_iou_restart(iou):
 
     iou.stop()