Fixes 164: properly set versions when de-dupeing

[jlsherrill]

on hooks you have to call SetColumn, you cannot just
update the attribute directly, even if it works for creation

[jlsherrill]

Create a repo:

curl -X POST http://localhost:8000/api/content_sources/v1/repositories/   -H "`scripts/header.sh 1 1`"  -d '{"url": "http://foo.com/bar", "versions": ["7"], "name": "foo"}'  -H "Content-Type: application/json"   -v

Then update it with duplicated versions (setting the right UUID):

 1137  curl -X PUT http://localhost:8000/api/content_sources/v1/repositories/29126567-ff05-4608-9bf4-4630148be298   -H "`scripts/header.sh 1 1`"  -d '{"url": "http://foo.com/bazr", "distribution_versions": ["7", "7"], "name": "foo2"}'  -H "Content-Type: application/json"   -v

Then fetch the repo:

curl -X GET http://localhost:8000/api/content_sources/v1/repositories/29126567-ff05-4608-9bf4-4630148be298  -H "`scripts/header.sh 1 1`" 

You shouldn't see duplicated versions, only "7"

[jlsherrill]

fixes this iqe test:

tests.test_repositories.test_create_update_distro_version_is_unique (from pytest)

AssertionError: assert ['8', '8'] == ['8']
  Left contains one more item: '8'
  Full diff:
  - ['8']
  + ['8', '8']

[jlsherrill]

https://issues.redhat.com/browse/HMSCONTENT-164

[mshriver]

Test failures aren't related to the intent of this PR, and are already being addressed.

The intended test failure has been addressed as demonstrated by the results in ci.int.devshift.
14:15:33 tests/test_repositories.py::test_create_update_distro_version_is_unique PASSED [ 96%]