updating hom_ref and hom_var to work with alternate ploidies

fixes #228 

these tests are all exactly the same, you are just changing the filename, genotype and truth you are checking for. *Extract Method* on it and create test cases that call it with the appropriate parameters. 

Also add tests for het() to make sure it still works even on the multi-ploidy file (it should hopefully return false, always). After you refactor the tests this will be a one-liner.