Consolidate behaviour of quarantine file uploads

Full story: https://www.pivotaltracker.com/story/show/42490007

TL;DR: File uploads now behave the same in all environments, i.e.
quarantine file storage is used everywhere. This also modifies the
behaviour of our uploaders such that the "path" methods reflect the
expected location for files on the filesystem whilst
simplifying and consolidating the configurarion of the uploads
behaviour.

Now that we are using quarantine file storage in all envs, files
uploaded in development will not be accessible in the browser until
they have been moved to the clean-uploads folder. We added the
development:fake_virus_scan rake task that copies files from
incoming-uploads to clean-uploads.
Tidy up upload access integration tests
Renamed clean_uploads_path to clean_uploads_root
QuarantineFileStorageSimulator no longer needed

Uploaded file storage now behaves the same in all environments, so
this magic is not necessary.
Add Whitehall.incoming_uploads_root
Move config out of CarrierWave and into Whitehall

Now both incoming and clean are configured in the same place and the
configuration is not coupled to carrierwave itself.
Remove unnecessary expand_path call from helper
test-quarantine is no longer used
Use a proper file lock for quarantine testing
Update test cleanup task to reflect new behaviour
Add addtional signposting of monkey-patch
Rake task to fake virus scan in development

Simply copies all incoming files to the clean folder, which is good
enough to simulate a successful virus scan.
fake_virus_scan rake task moves instead of copies

Avoids leaving duplicate files littered across the filesystem. Also
adds some logging output to show what is being done.
Segregate uploads during parallel test runs

Avoids parallel processes stomping on each other's uploads during
test runs. The nice side-effect of this is that we no longer need the
special-case cucumber tagging for testing virus checking.
Bulk upload behaves consistently during tests

Rather than monkey patching the default root directory for bulk
uploads in multiple places, we can set it according to the env during
initialisation. For consistency with attachment uploads, it's now
in tmp/test.
Merge pull request #617 from alphagov/carrierwave-debt

CarrierWave cleanup

* CarrierWave uploads now use the same storage mechanism in all environments.
* CarrierWave's path method now reports the actual location of (clean) uploads on the filesystem.
* There is a rake task to simulate the running of virus scanning in development- rake development:fake_virus_scan

https://www.pivotaltracker.com/story/show/42490007