Add tools/install_pip.sh

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

* Install distro setuptools if it not already present
* Install pip from source tarball as get-pip.py proved to be unreliable
* Remove python-distribute and python-pip from all prereq files,
  move python-setuptools to 'general'
* Remove the earlier unfubar_setuptppls() call that attenpted to fix this
* Only update requirements.txt when no changes in repo

Tested on Precise, F18 and CentOS6.
* Fedora and RHEL allow pip to install packages ON TOP OF RPM-installed
  packages.  THIS IS BROKEN.  And is one reason we have to be so picky
  about order and so forth.

Change-Id: Ibb4b42119dc2e51577c77bbbbffb110863e5324d
diff --git a/files/rpms/general b/files/rpms/general
index 9fa305c..2db31d1 100644
--- a/files/rpms/general
+++ b/files/rpms/general
@@ -11,7 +11,7 @@
 libxslt-devel # dist:rhel6 [2]
 psmisc
 pylint
-python-pip
+python-setuptools
 python-prettytable # dist:rhel6 [1]
 python-unittest2
 python-virtualenv