Add files in bin to tests

- Add __init__.py to bin so that those modules can be imported by tests.
- Add files in bin to coverage test.
Add skeleton test for bin/receiver

- Add skeleton test for bin/receiver so that the coverage stats become
  more accurate.
Add test_receiver to selective tests

- Add test_receiver to selective tests otherwise that unit test won't run
  and the coverage stats won't update for the modules in bin.
Add more tests for get_dns from receiver.py
Correct get_dns unit test
Merge pull request #14 from apel/bin-coverage

Add bin files coverage