Define Runner class

Define Runner class

It simply converts run_tests.py's functions to Runner's methods.
This proposal could be enhanced in a second step to fully leverage on
object programming.

It defines as instance variables the former static variables to allow
multiple runs (it's mandatory for unit testing).

All false positives in unit tests are fixed but run_tests.py is still
not fully covered.

Change-Id: I8f91c132aa8b2248041f31e46238dd5598344d34
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>