Improve configuration documentation
Improve configuration documentation

In each section, split required and optional parameters in their own
sub sections. Make it easier to craft a new configuration file from
scratch.

Have the setting explanation on its own indented paragraph to make it
easier to the eye (approved by my wife).

Add almost all missing settings based on the source code and document
some.

Document the Jenkins 'test-job' introduced in 861a5dbc by copy pasted
James E. Blair commit summary.

Change-Id: Iadaa0f70434cc254738b31359200c9fac02042bb

seandst/nodepool,citrix-openstack/nodepool,Tesora/tesora-nodepool,seandst/nodepool,citrix-openstack/nodepool,Tesora/tesora-nodepool