Enable logging if log_config_append is None

When default /etc/tempest/logging.conf is configured, tempest should
log. This patch appends the content from logging.conf to
log_config_append, if this config attribute is set, but has None set.

Change-Id: I7efa46b0c3b2c0ea722b2793cca6b57434923904
Closes-Bug: #1546536
1 file changed