[RTA/DPA BW tests] Fix HLT1 bandwidth test: use HLT1 input MDFs on eos rather than from the GRID for more I/O stability

Ross Hunterrequested to merge
rjhunter-bw-tests-use-hlt1-input-on-eos into master

Goes with lhcb/Moore!2903 (merged)

Main description there. Small changes here required for changing from DIGI to MDF input.

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