LP#1289450: OpenSRF 2.3.0 is the minimum required version

This patch updates the installation and upgrade documentation
to reflect the decision to make OpenSRF 2.3.0 be the minimum
required version.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Remington Steed <rjs7@calvin.edu>