A blank user agent is considered == to an empty string. When no -ping-user-agent option is specified, this is considered to be an empty string.
This reveals two problems:
- When no ping-user-agent is specified, main.go sets up a health check user agent of ""
- When no user agent is specified, the empty string is still checked against the health check user agents.
Now the health check middleware ignores blank user agents and paths in order to sanitise it's input to avoid this issue.
Additional tests have been added to verify these situations.
Moves the logic for redirecting to HTTPs to a middleware package and adds tests for this logic.
Also makes the functionality more useful, previously it always redirected to the HTTPS address of the proxy, which may not have been intended, now it will redirect based on if a port is provided in the URL (assume public facing 80 to 443 or 4180 to 8443 for example)
