Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1658566

Description of problem:
Generated report file has MIME type text/plain rather than text/csv (as opposed to e.g. exported host list [Hosts -> All Hosts -> Export] which is correctly text/csv).

Version-Release number of selected component (if applicable):
Tried on Sat 6.5 snap 7

How reproducible:
Deterministic

Steps to Reproduce:
1. Monitor -> Report Templates
2. Click Generate for some template
3. Submit

Actual results:
Download starts, type is shown as text/plain

Expected results:
Download starts, type is shown as text/csv