Link the payload test into all.

Testing Done:
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test/base:all
09:01:48 00:00   [test]
09:01:48 00:00     [pytest]
09:01:48 00:00       [run]
                     ============== test session starts ===============
                     platform linux3 -- Python 2.6.8 -- py-1.4.20 -- pytest-2.5.2
                     plugins: cov, timeout
                     collected 65 items

                     tests/python/pants_test/base/test_double_dag.py ....
                     tests/python/pants_test/base/test_abbreviate_target_ids.py ....
                     tests/python/pants_test/base/test_cmd_line_spec_parser.py .....
                     tests/python/pants_test/base/test_generator.py ....
                     tests/python/pants_test/base/test_build_invalidator.py .
                     tests/python/pants_test/base/test_payload.py ...
                     tests/python/pants_test/base/test_build_file_parser.py ............
                     tests/python/pants_test/base/test_run_info.py ..
                     tests/python/pants_test/base/test_address.py ........
                     tests/python/pants_test/base/test_hash_utils.py ..
                     tests/python/pants_test/base/test_build_root.py ......
                     tests/python/pants_test/base/test_revision.py ......
                     tests/python/pants_test/base/test_build_file.py ........

                     =========== 65 passed in 0.45 seconds ============

09:02:21 00:33     [junit]
09:02:21 00:33     [specs]
               SUCCESS

Also:
$ comm -3 <(grep -A17 "name = 'base'" tests/python/pants_test/base/BUILD | grep pants | cut -d: -f2 | cut -d\' -f1 | sort) <(./pants goal list tests/python/pants_test/base: | cut -d: -f2 | sort)
	all
	base
	context_utils

The all and base targets are aggregators and context_utils is a python_library so linkage in base is now full.

Bugs closed: 285

Reviewed at https://rbcommons.com/s/twitter/r/602/