Ruby test updates

* Added 'GENOTYPE_TEST_DATA' environment variable to denote path for non-public test data
* Consolidated multiple, identical data_path functions into one instance in test_helper.rb
* Added test_g2i_normalize to test the manifest normalization "side effect" of g2i
* Moved the zcall_test directory used by test_zcall_tasks.rb into the main GENOTYPE_TEST_DATA directory