default settings.LOGS_DIR to working directory

Without a default LOGS_DIR value, integration tests require LOGS_DIR
environment variable to be set, and fail with a Python exception
otherwise.

Change-Id: Ia9bc640f8b870df34e9380f1ec4c804d7204fc90
Closes-bug: #1299287
Signed-off-by: Dmitry Borodaenko <dborodaenko@mirantis.com>
Merge "default settings.LOGS_DIR to working directory"