Enhancements to installation script: --version and --uninstall

Use case

User might wish to control which rally version is installed or even purge rally from the machine completely.

Problem description

  1. Installation script doesn’t allow to choose version.
  2. No un-install support.

Possible solution

  1. Add --version option to installation script.
  2. Add --uninstall option to installation script or create an un-installation script