mw/kubernetes: rewrite parseRequest

Stop looking at the qtype in parseRequest and make k.Namespace a map.
Fallout from this is that pkg/strings as it is not used anymore. Also
add a few helper functions to make unexposed namespaces easier to see in
the code.

Add wildcard tests to the middleware tests.

middleware/pkg/strings/slice.go

@@ -1,11 +0,0 @@
-package strings
-
-// StringInSlice check whether string a is a member of slice.
-func StringInSlice(a string, slice []string) bool {
-	for _, b := range slice {
-		if b == a {
-			return true
-		}
-	}
-	return false
-}