Add accept_hostkey=yes to git tasks

Made the changes as discussed in #82 but believe it causes ```/root/.ssh/ does not exist```

Minimal config created with protobox-web. Only thing changed is ```ssh: forward_agent: true```
https://gist.github.com/9579267

```
$ vagrant destroy
$ vagrant up
```

```
TASK: [repository | git | install git application] ****************************
failed: [localhost] => (item={'path': '/srv/www/web/test', 'name': 'repo-test', 'install': 1, 'options': {'pre_install': [], 'source': 'git@bitbucket.org:JDorman/test.git', 'provider': 'git', 'post_install': [], 'revision': 'master'}}) => {"failed": true, "item": {"install": 1, "name": "repo-test", "options": {"post_install": [], "pre_install": [], "provider": "git", "revision": "master", "source": "git@bitbucket.org:JDorman/test.git"}, "path": "/srv/www/web/test"}}
msg: /root/.ssh/ does not exist
```