Upgrades pip under virtualenv
Upgrades pip under virtualenv

The version of pip supported by python-virtualenv has issues in
environment under proxy, hence uninstalling python-virtualenv package
and installing the latest version using pip.

Change-Id: Id749c37ab7fefa96b35f11816b56b9def5ef4b08
Closes-Bug: 1421541

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