Reduce required usage of LocalPackagePool

Several sections of the code *required* a LocalPackagePool, but they
could still perform their operations with a standard PackagePool.

Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

cmd/mirror_update.go

@@ -2,6 +2,8 @@ package cmd
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
 	"strings"
 	"sync"
 
@@ -161,7 +163,16 @@ func aptlyMirrorUpdate(cmd *commander.Command, args []string) error {
 					var e error
 
 					// provision download location
-					task.TempDownPath, e = context.PackagePool().(aptly.LocalPackagePool).GenerateTempPath(task.File.Filename)
+					if pp, ok := context.PackagePool().(aptly.LocalPackagePool); ok {
+						task.TempDownPath, e = pp.GenerateTempPath(task.File.Filename)
+					} else {
+						var file *os.File
+						file, e = ioutil.TempFile("", task.File.Filename)
+						if e == nil {
+							task.TempDownPath = file.Name()
+							file.Close()
+						}
+					}
 					if e != nil {
 						pushError(e)
 						continue