remote-blackbox: Do not follow HTTP redirects

There are a couple of websites we scrape that simply redirect to another
name (e.g. _pyrocufflink.net_ → _dustin.hatch.name_, _tabitha.biz_ →
_hatchlearningcenter.org_).  For these, we want to track the
availability of the first step, not the last, especially with regard to
their certificate lifetimes.

group_vars/remote-blackbox.yml

@@ -6,6 +6,15 @@ blackbox_modules:
         Accept-Charset: utf-8
         Accept-Language: en-US
       method: GET
+      follow_redirects: false
+      valid_status_codes:
+      - 200
+      - 301
+      - 302
+      - 303
+      - 304
+      - 307
+      - 308
     prober: http
     timeout: 5s