Remove duplicated isset function
Remove duplicated isset function

stackrc defines the isset function, but this function is already
declared in functions-common.

The stackrc sources the `functions` which sources the `functions-common`.

Change-Id: I0772c42d049833334107c2e6da3700e544ce094f

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