Make gitignore matching in rpzrecurse more precise

The pre-defined test cases use named.$TESTCASE.conf naming convention,
where TESTCASE is a human readable name contaning actual word(s). The
autogenerated test cases' names always start with a number from 1 to 6.

(cherry picked from commit e03daf22ec)

bin/tests/system/rpzrecurse/ns2/.gitignore

@@ -1,3 +1,8 @@
 /*.local
 /*.queries
-/*.conf
+/named.1*.conf
+/named.2*.conf
+/named.3*.conf
+/named.4*.conf
+/named.5*.conf
+/named.6*.conf