Fix variable typo of use_syslog in lib/tempest
Fix variable typo of use_syslog in lib/tempest

TEMPEST_CONF is not set but used it. As a result the meaningless file
'DEFAULT' is created. So this commit fixes to use proper variable name.

Closes-bug: #1394969
Change-Id: If6e58f269319df3c4f71b4fc13aa855c63f7e3a3

pacinete/devstack,dirkmueller/devstack,HPCHub/devstack,mmasaki/devstack,dtroyer/devstack,richliu/devstack,vishnugonela/devstack,CloudServer/devstack,rushiagr/devstack,wenhuizhang/devstack,j4/devstack,TwinkleChawla/devstack,parul24/devstack,nuxeh/devstack,olivierlemasle/devstack,andrewrothstein/devstack,openstack-dev/devstack,bljgaurav/openstack-test,atulpatil301/devstack,olivierlemasle/devstack,avvocatodemarchis/devstack,ozamiatin/devstack,bswartz/devstack,TwinkleChawla/devstack,andrewrothstein/devstack,parul24/devstack,eharney/devstack,prithivm/branch01,sequenceiq/devstack,bigswitch/devstack,upadhyay-prashant/devstack,neerja28/Devstack_GlusterFS,avvocatodemarchis/devstack,upadhyay-prashant/devstack,eharney/devstack,dtroyer/devstack,thomasem/devstack,nawawi/openstack,openstack-dev/devstack,LoHChina/devstack,herrsechs/devstack,mssumanth/devstack,nuxeh/devstack,BSJAIN92/OpenStack,noironetworks/devstack,pombredanne/devstack,mmasaki/devstack,flavio-fernandes/devstack,mssumanth/devstack,costingalan/devstack,samgoon/devstack,promptworks/devstack,bigswitch/devstack,bswartz/devstack,thomasem/devstack,pczerkas/devstack,j4/devstack,varunarya10/devstack,kplus/devstack-moonshot,HPCHub/devstack,varunarya10/devstack,bq-xiao/devstack,kplus/devstack-moonshot,LoHChina/devstack,samgoon/devstack,affo/devstack,pacinete/devstack,rushiagr/devstack,sc68cal/devstack,wenhuizhang/devstack,sequenceiq/devstack,Mahito/devstack,pombredanne/devstack,richliu/devstack,sc68cal/devstack,noironetworks/devstack,liuquansheng47/devstack,dirkmueller/devstack,herrsechs/devstack,prithivm/branch01,atulpatil301/devstack,mc2014/devstack,bljgaurav/openstack-test,NaokiMiyata/devstack,NaokiMiyata/devstack,vsham20/devstack,neerja28/Devstack_GlusterFS,pczerkas/devstack,CloudServer/devstack,group-policy/devstack,affo/devstack,vsham20/devstack,bq-xiao/devstack,promptworks/devstack,Mahito/devstack,vishnugonela/devstack,BSJAIN92/OpenStack,liuquansheng47/devstack,mc2014/devstack,costingalan/devstack,group-policy/devstack,ozamiatin/devstack,nawawi/openstack,flavio-fernandes/devstack