CA-108508: Add a script to re-enable the RRDD plugin data sources

Script is 'xe-enable-all-plugin-metrics', which takes a single
argument 'true' or 'false'. This script will restart the toolstack.

Signed-off-by: Jon Ludlam <jonathan.ludlam@eu.citrix.com>
Merge pull request #1297 from jonludlam/add-rrdd-enabling-script

CA-108508: Add a script to re-enable the RRDD plugin data sources