MFC r293048,r293444:

r293048:

• Use a temporary file for the temporary md(4) devices instead of hardcoding it
• Remove the temporary file in the cleanup routine

r293444:

• Move functions that might be used in class-specific cleanup functions (geom_test_cleanup, etc) down so the testcases don't emit noise when bailing
• Conform to the TAP protocol better when dealing with classes that can't be loaded and with temporary files that can't be allocated for tracking md(4) devices.