Add brunel.initial-time test

Runs exactly the same test as brunel.2017magup, but with a different IntialTime. If initialisation is done correctly, output should be identical, but that is currently not the case.

The test shares the reference file with brunel.2017magup. For this reason it runs before 2017magup, to avoid over-writing the 2017magup.ref.new reference file when it needs updating

N.B. This test explicitly tests the Muon initialisation issue described in LHCBPS-1800 and its workaround in Rec!1154 (merged) by choosing an InitialTime outside of a fill.