TDML tests pollute temporary directories

The TMDL runner create many TDML files. For example, embedded schema tests create tmp file. And runtime2 generate files are also created in /tmp. We aren't very consistent about where these tmp files are create, often times just creating files directly in /tmp. This pollutes tmp pretty badly. We should isntead create all tmp files in a subdirectory (e.g. /tmp/daffodil-test/). Additionally, we need to ensure we clean up temporary files when each test is complete.