Make changes to provisioning and wiki to reflect LAVA 2018.4

Issue Background

stretch.backports has been updated so that it now installs LAVA 2018.4, this requires changes to our scripts

Issue description

Python 3 is now used so configure_lava.sh breaks Health checks now created without the UI

Acceptance criteria

• Updates provision scripts
• Update wiki to document how to create a health check
• Update wiki to document how to re-run a health check
• Update wiki to link in new example output