Clean up sortedKeys function

This introduces a generic function SortedStringKeys which can be used to
get a slice of sorted string keys for all kinds of maps having string
keys.

Bug: N/A
Test: m
Change-Id: I542194c68984d909b7ad1dbf060d4d3a98f0ef23
diff --git a/android/util.go b/android/util.go
index f7a3437..3b8bc78 100644
--- a/android/util.go
+++ b/android/util.go
@@ -16,6 +16,7 @@
 
 import (
 	"fmt"
+	"reflect"
 	"regexp"
 	"runtime"
 	"sort"
@@ -77,10 +78,15 @@
 	return string(ret)
 }
 
-func sortedKeys(m map[string][]string) []string {
-	s := make([]string, 0, len(m))
-	for k := range m {
-		s = append(s, k)
+func SortedStringKeys(m interface{}) []string {
+	v := reflect.ValueOf(m)
+	if v.Kind() != reflect.Map {
+		panic(fmt.Sprintf("%#v is not a map", m))
+	}
+	keys := v.MapKeys()
+	s := make([]string, 0, len(keys))
+	for _, key := range keys {
+		s = append(s, key.String())
 	}
 	sort.Strings(s)
 	return s