strengthen tile metadata file regexp matcher

Some tile zips contain the `metadata/` folder as a separate "file"
as well. This gets caught in the current `metadata/.*` matcher for the
metadata file.

Add this empty directory to our test, and modify the regexp to more
strongly match the expected metadata yml file.

[fixes #239]

[#160019619] pivotal-cf/om #239: tile-metadata throws EOFs on many tiles

commands/tile_metadata.go

@@ -41,7 +41,7 @@ func (t TileMetadata) Execute(args []string) error {
 	defer file.Close()
 
 	for _, f := range file.File {
-		matched, err := regexp.MatchString("metadata/.*", f.Name)
+		matched, err := regexp.MatchString("metadata/.+\\.yml", f.Name)
 		if err != nil {
 			return fmt.Errorf("failed to match file name regex: %s", err)
 		}

commands/tile_metadata_test.go

@@ -33,6 +33,13 @@ var _ = Describe("TileMetadata", func() {
 			productFile, err = ioutil.TempFile("", "fake-tile")
 			z := zip.NewWriter(productFile)
 
+			// https://github.com/pivotal-cf/om/issues/239
+			// writing a "directory" as well, because some tiles seem to
+			// have this as a separate file in the zip, which influences the regexp
+			// needed to capture the metadata file
+			_, err := z.Create("metadata/")
+			Expect(err).NotTo(HaveOccurred())
+
 			f, err := z.Create("metadata/fake-tile.yml")
 			Expect(err).NotTo(HaveOccurred())