Fixed check method of $USE_GET_PIP
Fixed check method of $USE_GET_PIP

'[[ -n "$USE_GET_PIP" ]]' always TRUE
because $USE_GET_PIP is '0' or '1'.

Change-Id: I73c4c6befe2126882ef21991b2a3fe712b2ac388
Closes-Bug: #1259824

upadhyay-prashant/devstack,HPCHub/devstack,virtualopensystems/devstack,Juniper/devstack,liuquansheng47/devstack,pacinete/devstack,j4/devstack,flavio-fernandes/devstack,prithivm/branch01,wenhuizhang/devstack,eshnil2000/devstack,openstack-dev/devstack,dtroyer/devstack,neerja28/Devstack_GlusterFS,group-policy/devstack,herrsechs/devstack,bigswitch/devstack,mssumanth/devstack,eharney/devstack,LoHChina/devstack,eharney/devstack,atulpatil301/devstack,varunarya10/devstack,bq-xiao/devstack,parul24/devstack,herrsechs/devstack,pacinete/devstack,pombredanne/devstack,LoHChina/devstack,varunarya10/devstack,yamt/devstack,prithivm/branch01,nawawi/openstack,ozamiatin/devstack,affo/devstack,bljgaurav/openstack-test,vsham20/devstack,mc2014/devstack,bigswitch/devstack,richliu/devstack,neerja28/Devstack_GlusterFS,ozamiatin/devstack,wenhuizhang/devstack,innodee/openstackk,thomasem/devstack,flavio-fernandes/devstack,samgoon/devstack,noironetworks/devstack,richliu/devstack,mssumanth/devstack,nuxeh/devstack,olivierlemasle/devstack,openstack-dev/devstack,Millnert/contrail-devstack,j4/devstack,bswartz/devstack,TwinkleChawla/devstack,rushiagr/devstack,vsham20/devstack,mmasaki/devstack,JioCloud/devstack,thomasem/devstack,nawawi/openstack,BSJAIN92/OpenStack,sequenceiq/devstack,pczerkas/devstack,TwinkleChawla/devstack,Mahito/devstack,pombredanne/devstack,kplus/devstack-moonshot,rushiagr/devstack,vishnugonela/devstack,olivierlemasle/devstack,bq-xiao/devstack,pczerkas/devstack,andrewrothstein/devstack,sc68cal/devstack,jamielennox/devstack,tianweizhang/devstack,promptworks/devstack,vishnugonela/devstack,sc68cal/devstack,CloudServer/devstack,dirkmueller/devstack,costingalan/devstack,andrewrothstein/devstack,NaokiMiyata/devstack,promptworks/devstack,dirkmueller/devstack,mc2014/devstack,bljgaurav/openstack-test,samgoon/devstack,dtroyer/devstack,upadhyay-prashant/devstack,tianweizhang/devstack,mmasaki/devstack,BSJAIN92/OpenStack,noironetworks/devstack,avvocatodemarchis/devstack,CloudServer/devstack,srics/devstack,costingalan/devstack,nuxeh/devstack,HPCHub/devstack,sequenceiq/devstack,williamthegrey/devstack,bswartz/devstack,avvocatodemarchis/devstack,kplus/devstack-moonshot,parul24/devstack,affo/devstack,Mahito/devstack,group-policy/devstack,atulpatil301/devstack,NaokiMiyata/devstack,liuquansheng47/devstack