Add tools/install_pip.sh

Install a known working recent version of pip that handles
installation dependencies correctly.  Extracted to a separate script
so it can be used apart from stack.sh.

* Install pip from source tarball as get-pip.py proved to be unreliable

Tested on Precise, F18 and CentOS6.
* Fedora and RHEL allow pip to install packages ON TOP OF RPM-installed
  pacakges.  THIS IS BROKEN.  Preventing RPM from re-breaking things by
  installing on top of the pip-installed packages is being studied using
  a meta-rpm in another commit.

Known improvements:
* improve the pip version checking

Change-Id: Ibb4b42119dc2e51577c77bbbbffb110863e5324d
Merge branch 'install-pip' into dt-test
Merge branch 'nova-plugin' into dt-test
Merge branch 'docker' into dt-test
Merge branch 'image-member-exercise' into dt-test
Merge branch 'screen-stop' into dt-test
Merge branch 'doc-shocco-cleanup' into dt-test
Merge branch 'update-usb-tools' into dt-test