log: don't create foo.log
log: don't create foo.log

test_tempest_set_log_file was calling tempest_set_log_file and never
resetting this value. That caused some other test to create foo.log
and not clean it up.

Change-Id: I23efe8fb89531752b01bdf9c0fbdc39c77058a51

openstack/oslo.log