Install newer pip in install_rally.sh
Install newer pip in install_rally.sh

Newer pip is required to handle certain requirements correctly.

Closes-Bug: #1466055
Change-Id: I7f7fcd8a7f50e51d61677dd8126fec7016006caa

vefimova/rally,go-bears/rally,group-policy/rally,cernops/rally,openstack/rally,eonpatapon/rally,vefimova/rally,afaheem88/rally,aforalee/RRally,openstack/rally,gluke77/rally,eayunstack/rally,redhat-openstack/rally,vganapath/rally,aplanas/rally,afaheem88/rally,aplanas/rally,yeming233/rally,yeming233/rally,paboldin/rally,gluke77/rally,vganapath/rally,vganapath/rally,pyKun/rally,gluke77/rally,go-bears/rally,amit0701/rally,aforalee/RRally,openstack/rally,eayunstack/rally,shdowofdeath/rally,group-policy/rally,vganapath/rally,eayunstack/rally,paboldin/rally,amit0701/rally,openstack/rally,shdowofdeath/rally,gluke77/rally,redhat-openstack/rally,paboldin/rally,cernops/rally,pyKun/rally,eonpatapon/rally,group-policy/rally,amit0701/rally