Description of problem:
On removing a product with many repositories, candlepin throws a number of exceptions (probably due to a race condition).

This leads to a failed task which stays in paused state and blocks other related tasks (e.g. organization removal).
Resuming the task sometimes works.



Version-Release number of selected component (if applicable):
6.2.0 Beta GA15.0

How reproducible:


Steps to Reproduce:
1. create an organization with some product
2. create many repositories inside this product
3. [optional] tail -f /var/log/candlepin/candlepin.log
4. delete the product (or an organization)

```
this simple loop should feed your product by 50 repos:
ORG=3
PROD=1
for i in {1..50}; do hammer --csv repository create --content-type puppet --name="foo_${i}" --organization-id ${ORG} --product-id ${PROD} --url="https://aaaaa.com/aaa/${i}"; done
```
- the URL length migh matter (or whatever that keeps candlepin more busy while processing the repo)

Actual results:
ERROR: duplicate key value violates unique constraint "cp_product_content_pkey"

Expected results:
- no SQL errors, product properly removed

Additional info: