Parsing of `--debug` on import

As pointed out by @carandraug  in gh-2477, if a separating `--` is not used before `--debug=ERROR` then the result is quite surprising: **more** is logged rather than **less*! This fixes that and another small issue noticed by @sbesson. To test check that all the login options of `bin/omero import` still function correctly and that the debug output matches the expectations of 2477.