Fix IP regex used in the "resolver" system test

If dots are not escaped in the "1.2.3.4" regular expressions used for
checking whether IP address 1.2.3.4 is present in the tested resolver's
answers, a COOKIE that matches such a regular expression will trigger a
false positive for the "resolver" system test.  Properly escape dots in
the aforementioned regular expressions to prevent that from happening.
40 jobs for !1568 with michal/fix-ip-regex-used-in-the-resolver-system-test in 17 minutes and 14 seconds (queued for 4 seconds)
merge request