Turning off offline compression for integration test

[Thai Tran]

We have COMPRESS_OFFLINE disabled by default in our tests in horizon, we need to do the same in dashboard.
Here is a very long explanation of why this needs to happen.

What we know about offline compression:
1. You need to manually run "manage.py compress" to generate the offline compressed files
2. The offline compressed files are stored in /static/dashboards/
3. There is a manifest file that maps a key to a file
4. The key is generated via some hashing mechanism based on content
5. When page request happens, the compressor looks up the manifest and hands over the compressed file
6. If you make changes inside of the {% compress %} tag, you NEED to manually rerun the compress cmd in #1

In summary, if you enable COMPRESS_OFFLINE, you need to manually generate the compressed files.
If you made changes to your compress tag, you need to rerun the compress command.

How is this related to integration test?
a. Integration tests will break if you made changes to the {% compress %} tag and did not rerun the compress command
b. The error is obscure and goes something like "OfflineGenerationError" and complains about not finding a key (#3)

To avoid future problems, integration tests should not have COMPRESS_OFFLINE enabled.
This is a feature for deployers to use for a STABLE environment.

Links:
https://github.com/openstack/horizon/blob/master/horizon/test/settings.py#L143
https://github.com/openstack/horizon/blob/master/openstack_dashboard/test/settings.py