Description of problem:
PUT /api/v2/discovered_hosts/reboot_all - returns response in plain text even though content-type is application/json

Version-Release number of selected component (if applicable):
Satellite 6.15.0 Snap 9

How reproducible:
Always

Steps to Reproduce:
1. # curl -X PUT -k -H 'Content-Type: application/json' -u admin:changeme -i 'https://satellite.example.com/api/v2/discovered_hosts/reboot_all'
2.
3.

Actual results:
Returned response is not valid json, it's plain text

Expected results:
Returned output is formatted as JSON

Additional info:
Jira issue https://issues.redhat.com/browse/SAT-20935