Reduce logging in the SFC test case

Reduce logging in the SFC test case

JIRA: FUNCTEST-446

Reduce the logs that appear in the Jenkins CI console to make the output
of the SFC test case more readable

- Redirect tacker installation logs to results folder
  /home/opnfv/functest/results/odl-sfc.log
- Split odl-sfc preparation into a new script
- Pipe STDERR in the sfc.py script so that "Added to known hosts"
  messages do not show in the output

Change-Id: Ibf871ade6827d4817f33623b935c5f1d904086bb
Signed-off-by: George Paraskevopoulos <geopar@intracom-telecom.com>