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/keystone b/files/rpms/keystone
index 33a4f47..52dbf47 100644
--- a/files/rpms/keystone
+++ b/files/rpms/keystone
@@ -4,10 +4,9 @@
 python-paste-deploy #dist:f16,f17,f18,f19
 python-paste-script #dist:f16,f17,f18,f19
 python-routes
-python-setuptools   #dist:f16,f17,f18,f19
 python-sqlalchemy
 python-sqlite2
 python-webob
 sqlite
 
-# Deps installed via pip for RHEL
\ No newline at end of file
+# Deps installed via pip for RHEL