Description of problem:

Whenever I run multiple POST requests to create discovery rules in parralel, I ocassionally get a 201 response with a different payload format.
I’m unable to reproduce this if I execute the requests sequentially. More parralel requests I execute, bigger change of hitting this issue:

{"discovery_rule":{"id":742,"name":"57531206","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":29227,"enabled":true,"created_at":"2020-09-16T10:33:11.220Z","updated_at":"2020-09-16T10:33:11.220Z"}}
{"id":745,"name":"304796992","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":17120,"enabled":true,"created_at":"2020-09-16T10:33:12.128Z","updated_at":"2020-09-16T10:33:12.128Z"}


I provided logs and reproducer here:
https://community.theforeman.org/t/different-response-format-on-identical-requests-when-executed-in-parralel/20511


Version-Release number of selected component (if applicable):
6.8.0-15

How reproducible:
on concurrent POST requests to /discovery_rules

Steps to Reproduce:
1. create an org, location and a hostgroup which you want to associate your rules with
2. run the following example in multiple shells (3-4):

for i in {1..10}; do curl -sku admin:changeme -H "content-type: application/json" -d "{\"name\": \"$RANDOM$RANDOM\", \"hostname\": \"myhost-<%= rand(99999) %>\", \"priority\": $RANDOM, \"hostgroup_id\": 125, \"location_ids\": [259], \"organization_ids\": [255], \"search\": \"memory > 500\"}" https://<sat_server>/api/v2/discovery_rules; echo ""; done

Actual results:
some responses use different payload format:

{"id":2969,"name":"93955553","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":18417,"enabled":true,"created_at":"2020-09-16T14:51:28.870Z","updated_at":"2020-09-16T14:51:28.870Z"}
{"id":2972,"name":"102037951","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":10731,"enabled":true,"created_at":"2020-09-16T14:51:29.796Z","updated_at":"2020-09-16T14:51:29.796Z"}
{"discovery_rule":{"id":2975,"name":"103111213","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":16633,"enabled":true,"created_at":"2020-09-16T14:51:30.869Z","updated_at":"2020-09-16T14:51:30.869Z"}}
^^^
{"id":2977,"name":"179169626","search":"foo","hostgroup_id":125,"hostname":"foo","max_count":0,"priority":15149,"enabled":true,"created_at":"2020-09-16T14:51:31.881Z","updated_at":"2020-09-16T14:51:31.881Z"}


Expected results:
ALL responses should use consistent format