Add tools/install_pip.sh

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

* Remove all packaged setuptools, distribute and pip installations as
  they will just get in the way.
* Install setuptools from source using ez_setup.py
* Install pip from source tarball as get-pip.py proved to be unreliable

Tested on Precise, F18 and CentOS6.

Known improvements:
* improve the pip version checking

Change-Id: Ibb4b42119dc2e51577c77bbbbffb110863e5324d
Merge branch 'install-pip' 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