Add the install_rally.sh file

The install_rally.sh file is a Bash script that installs Rally on a
Unix system. Specifically, it is able to install and configure Rally
either globally (system-wide, the default behavior), or isolated in a
virtual environment using the virtualenv tool.

Change-Id: I4b6498a52cb1105fd8e27593ac482038ddcff702
Implements: blueprint rally-installation-script
Merge "Add the install_rally.sh file"