Adding extra_hosts param to docker-compose

[immortal-tofu]

Adding extra_hosts parameter with doc and tests

[dnephin]

Please keep this list sorted alphabetically (same with the list below)

[dnephin]

rebase with master to pickup the fix for those test failures, otherwise looks good

[immortal-tofu]

Rebase done

[immortal-tofu]

Fixed alphabetical order too

[aanand]

Test appears to be failing:

FAIL: test_create_container_with_extra_hosts (tests.integration.service_test.ServiceTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/code/tests/integration/service_test.py", line 144, in test_create_container_with_extra_hosts
    ['myserver:192.168.2.90', 'myserver2:10.55.32.12'])
AssertionError: None != [u'myserver:192.168.2.90', u'myserver2:10.55.32.12']

[dnephin]

I think this feature requires docker 1.3 (http://docs.docker.com/v1.3/release-notes/), and if I remember correctly wercker is running docker 1.2, so I think this is blocking on #886 as well

[immortal-tofu]

Closed since this feature exists now in docker-compose.