Re-assert disabled tests
    
    As per upstreams advice[0] I excluded certain tests that we cannot run
    using markers. Some of the remaining tests either require network or
    some other setup, which prohibits us from running those.
    
    Three tests, however, fail without a clear reason. I disabled those, but
    also asked upstream[0].
    
    [0] https://github.com/pauldmccarthy/fslpy/issues/17