Change TestCF1_7 inheritance, alter CF test helper
Change TestCF1_7 inheritance, alter CF test helper

Changes TestCF1_7 to not inherity from TestCF1_6, which would cause many
redundant tests being re-run.  Moves `get_result` helper function out of
TestCF1_6 class.

aodn/compliance-checker,ioos/compliance-checker,lukecampbell/compliance-checker,ocefpaf/compliance-checker