curl_tests: Redirect any request to the incus container

[fflorent]

Problem

When creating custom domains in the tests, the curl tests don't recognize them as being part of the incus container and does not request it.

Solution

Use wildcard to redirect all the domains to the incus container. Quoting this documentation:

Specify the host as a single asterisk (*) to match all names. This wildcard is resolved last so any resolve with a specific host and port number is given priority.