* tests/test_selfhosting_utils.[h|cc]:
Add test_all_hosting_modes().
        * tests/test_selfhosting_new_empty.cc:
        * tests/test_selfhosting_new_empty_change_sysprefs.cc:
        * tests/test_selfhosting_new_empty_then_users.cc:
        * tests/test_selfhosting_new_from_example.cc:
        * tests/test_selfhosting_new_from_example_operator.cc:
        * tests/test_selfhosting_new_from_example_strangepath.cc:
        * tests/test_selfhosting_new_then_alter_table.cc:
        * tests/test_selfhosting_new_then_change_columns.cc:
        * tests/test_selfhosting_new_then_choices.cc:
        * tests/test_selfhosting_new_then_image.cc:
        * tests/test_selfhosting_new_then_lookup.cc:
        * tests/test_selfhosting_new_then_report.cc:
        * tests/test_selfhosting_non_numeric_primary_keys.cc:
        * tests/test_selfhosting_sqlinjection.cc: Use this,
passing a callback slot, instead of having the same repeated
code in each file.