Merge branch 'fix_operator_test' into 'NIFTy_7'

Make Nonlinear operator test accept Operators

See merge request !570
12 jobs for NIFTy_7 in 27 minutes and 28 seconds (queued for 3 seconds)
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build_docker_from_scratch

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  Test
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test_mpi

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test_serial

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run_bernoulli

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run_visual_mgvi

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