With the new in-band inspection, we can derive the callback URL from
the Ironic URL, there is no need to duplicate it. This change uses
the presence of collectors as a sign to run inspection.
The previous approach of setting an inspection URL, with or without
explicitly setting collectors, still works for compatibility with
ironic-inspector.
Change-Id: Ie4279ee6d2995c9686f1dcdef1d6e5dc1dd20871