Convert test_pkg to use unittest.

Lib/test/output/test_pkg

-test_pkg
-running test t1
-running test t2
-t2 loading
-doc for t2
-t2.sub.subsub loading
-t2 t2.sub t2.sub.subsub
-['sub', 't2']
-t2.sub t2.sub.subsub
-t2.sub.subsub
-['spam', 'sub', 'subsub', 't2']
-t2 t2.sub t2.sub.subsub
-['spam', 'sub', 'subsub', 't2']
-running test t3
-t3 loading
-t3.sub.subsub loading
-t3 t3.sub t3.sub.subsub
-running test t4
-t4 loading
-t4.sub.subsub loading
-t4.sub.subsub.spam = 1
-running test t5
-t5.foo loading
-t5.string loading
-1
-['foo', 'string', 't5']
-['__doc__', '__file__', '__name__', '__path__', 'foo', 'string', 't5']
-['__doc__', '__file__', '__name__', 'string']
-['__doc__', '__file__', '__name__', 'spam']
-running test t6
-['__all__', '__doc__', '__file__', '__name__', '__path__']
-t6.spam loading
-t6.ham loading
-t6.eggs loading
-['__all__', '__doc__', '__file__', '__name__', '__path__', 'eggs', 'ham', 'spam']
-['eggs', 'ham', 'spam', 't6']
-running test t7
-t7 loading
-['__doc__', '__file__', '__name__', '__path__']
-['__doc__', '__file__', '__name__', '__path__']
-t7.sub.subsub loading
-['__doc__', '__file__', '__name__', '__path__', 'spam']
-t7.sub.subsub.spam = 1