Add Functest Logger centralized Class

Add Functest Logger centralized Class

JIRA: FUNCTEST-228

This is to be used by all the scripts using logging mechanisms.
Usage:

  import functest_logger as fl
  logger = fl.Logger("<script_name>").getLogger()

  # treat it as a normal logger object, as before:
  logger.info("message to be shown with - INFO - ")
  logger.debug("message to be shown with - DEBUG -")

Change-Id: I94e248523bc9bc148c9d171c978804b5d1865dd9
Signed-off-by: jose.lausuch <jose.lausuch@ericsson.com>