The function get_pip upgrades the pip packages for pip. If OSA is
updated to require newer versions these may not be present on the repo
server and this will cause bootstrap-ansible.sh to fail.
Update the get_pip function to fallback on calling pip with the
--isolated flag when pip is installed and the pip packages are being
upgraded.
Change-Id: Ifa644b9bf6aa8b20028eb0257c40fe20f3ab1a3b