Use 'which pip' rather than /usr/bin/pip
Use 'which pip' rather than /usr/bin/pip

Bug 1095472: Bugfix to use 'which pip' rather than assume pip always lives in /usr/bin

Change-Id: I0cc8a5e35306372653c3c27da9504c64e39d56dd

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