Change instructions to use get-pip
Change instructions to use get-pip

If you're going to install software using pip, then it means you're
willing to use pip to install software. If you are willing to do that,
then installing the latest pip via pip is completely reasonable. The
distro pip will often be too old or broken to work properly.

Closes-Bug: #1481085
Change-Id: If161c04aac30f489162cd72a329f71ddbe5635d6

eshijia/SUR,Tennyson53/SUR,mjbrewer/testindex,dimtruck/magnum,Alzon/SUR,dimtruck/magnum,Alzon/SUR,openstack/magnum,Tennyson53/magnum,Tennyson53/SUR,mjbrewer/testindex,Tennyson53/magnum,mjbrewer/testindex,ArchiFleKs/magnum,jay-lau/magnum,ArchiFleKs/magnum,openstack/magnum,eshijia/SUR,eshijia/magnum,eshijia/magnum