DevVM now lives in pp-puppet

We've moved the dev vm and this replicate script was still referencing
the old location. It now needs to explicitly say development-1 as there
are multiple VMs attached to that Vagrantfile.
Add deprecation warning for write API by name

We "deprecated" using the `/data-set-name` URL some time ago in favour
of `/data-group/data-type`. This is the first step towards actually
deprecating it - make some noise about it now.
Merge pull request #273 from alphagov/fix-replicate-db

DevVM now lives in pp-puppet
Merge pull request #274 from alphagov/add-deprecation-warning

Add deprecation warning for write API by name
Use abort() for error handling

This will make it easier to refactor common code when we implement the
data-set emptying endpoint.

Also modify exception handler to extract the description from the
HTTPError, rather than the name
Refactor the way POSTs are validated and handled

- split validation of data-set existence and authorization into two
  helpers
- rename _write_to_data_set to _append_to_data_set due to the fact that
  it's called by a POST, and we will implement a "set" (PUT) later.
- change signature of _append_to_data_set to take data as an argument,
  rather than the function extracting it from the global request object
  (side effect, meh)