Enforce order and style of imports

Done using isort[1], with the following command:
```
isort -rc ./app ./tests
```

Adds linting to the `run_tests.sh` script to stop badly-sorted imports
getting re-introduced.

Chosen style is ‘Vertical Hanging Indent’ with trailing commas, because
I think it gives the cleanest diffs, eg:
```
from third_party import (
    lib1,
    lib2,
    lib3,
    lib4,
)
```

1. https://pypi.python.org/pypi/isort

app/cloudfoundry_config.py

@@ -3,8 +3,8 @@ Extracts cloudfoundry config from its json and populates the environment variabl
 on local/aws boxes
 """
 
-import os
 import json
+import os
 
 
 def extract_cloudfoundry_config():