Document order of Openstack resources' list
Document order of Openstack resources' list

The order of the resources' list that ospurge deletes corresponds to the
order in which ospurge actually deletes the resources (taking into
account inter-resources dependencies). Documenting this into the code
should help contributors to add resources at the proper location.

Change-Id: Icc691b8dcc94944a2cc72ac24fae738210e6622f

DigitalPacific/ospurge,remoteur/ospurge,tnahak/ospurge,openstack/ospurge,stackforge/ospurge,openstack/ospurge,JonasPf/ospurge