[BUG] Reflected XSS

[discodamone]

I would have reported this privately but there is no security policy for this repo.

Describe the bug
Reflected XSS at /render/?cacheTimeout=<img%20src=x%20onerror=alert(document.domain)> due to an error message that doesn't sanitize the output when cacheTimeout is not an integer.

To Reproduce
Run the server, visit /render/?cacheTimeout=<img%20src=x%20onerror=alert(document.domain)>

Expected behavior
Output the error with no HTML tags allowed

Environment (please complete the following information):
I ran docker with graphite 1.10.0

[deniszh]

Looks like fixed in #2782