Fix get_pip_command()
Fix get_pip_command()

Be more flexible in finding pip, especially after we start replacing it

Change-Id: I14b0ac1584aab99c2fe58a78e3a43196ae8130ca

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