Simplify logging

Simplify logging

In order to collect logs from features running through
functest framework (mainly for troubleshooting purposes),
the logging mechanism has been updated accordingly.

It should be noted that feature logs are printed in functest.log.
All logs are now printed in functest.log whatever the namespace.

JIRA: SFC-125

Co-Authored-By: Cédric Ollivier <cedric.ollivier@orange.com>
Change-Id: I6cb32e5553749023d490d553ae4653750c52e844
Signed-off-by: Panagiotis Karalis <pkaralis@intracom-telecom.com>
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
(cherry picked from commit ceaea7f0cb95bce7f71d29dff71d58654cf0e700)