Refactor SFC testcase

Refactor SFC testcase

- Change the way the test checks if the vxlan_tool has started.
  Now the vxlan_tool is detected even if another python process is up.
- Log the exceptions in the vxlan_tool check block. The exceptions that
  occur are not destructive for the testcase but it's better to be
  visible.
- Add a 60 seconds sleep before the testcase starts to give plenty of
  time to ODL to add the correct flows.
- Move the testcase success/fail check blocks inside the try blocks.
  The checks are performed on the stdout variable which is in scope
  only inside the try blocks.

Change-Id: I49dec176fb83117e9896ac1d19e8a5bd95e3d7cf
Signed-off-by: George Paraskevopoulos <geopar@intracom-telecom.com>
(cherry picked from commit 563a540585768d900d70ce79f2a871a9d1fab03e)