Rename fixtures directory to job_fixtures to prepare for adding view_fixtures
directory in the following commits.
Change-Id: Ic20997cae020b542ddc22bf444fa6b92fbcae064
Prefer user defined macros over inbuilt entry points, as JJB may
accidentally use a name that has already been used by an end-user to
define a custom macro.
Warn users when they have a macro defined that masks an in-built
component to avoid accidentally changing XML generated with new
releases.
Change-Id: I6cae62d7cc40be6c4a5636a74f151fcce4cdd856