Create temp file in setUp() to avoid warning
Create temp file in setUp() to avoid warning

The tempfile in test_unwatch_log() generates a warning
in the 'cover' tests:

sys:1: ResourceWarning: unclosed file
<_io.TextIOWrapper name='/var/tmp/tmpz1l83cix/tmpjz5uavc7/
 watch_log_temp_file_name' mode='a' encoding='UTF-8'>

Create it in setUp() which will trigger an automatic
cleanup on test completion.

Trivialfix

Change-Id: I816ac65a935250f8606dba75d7080eb9c384fceb

mahak/neutron,openstack/neutron,openstack/neutron,mahak/neutron,openstack/neutron,noironetworks/neutron,noironetworks/neutron,mahak/neutron