Issue title: List of tasks is not updated after switching fabfile
 Issue body: I set FABFILE_PATH in the settings.py but the task dropdown in the project stage does not reflect the new tasks. When I just pick one of the shown (default) tasks for deployment, I receive an error as the task is not known and I'm shown the list of new tasks as "available commands":

```
Warning: Command(s) not found:
    git_pull

Available commands:

    adm_change_branch   Changes git branch and updates
    adm_git_pull        Does a git stash then a git pull on the project
    adm_restart_cira    Restart the web server
    adm_restart_sentry  Restart Sentry
    adm_update          Does a git pull and restarts the web server
    restart_celery      Restart the Celery
```
![image](https://cloud.githubusercontent.com/assets/536913/11060456/abd419a2-87a0-11e5-93c7-e89872953430.png)

So FB takes the correct tasks but does not show them in the frontend.
 Comments: 
 Comment 0: Nevermind, I disabled the caching for testing and the tasks were shown correctly. I added the following code to the settings.py to flush the cache on every restart.

```python
from django.conf import settings
settings.configure(CACHES=CACHES)

from django.core.cache import cache
cache.clear()
```
{'source': 'GithubIssues', 'repo_name_with_owner': 'fabric-bolt/fabric-bolt', 'issue_id': 116082100, 'repo_stars': 215.0}