Check for OS Type and skip within the test

Premature check for OS type means that the test
will never even get to run on other OS types. This
will cause it to be always flagged as a failure on
such OS types.

Signed-off-by: vikrambirsingh <vikrambir.singh@docker.com>

integration/plugin/volumes/main_test.go

@@ -19,9 +19,6 @@ func TestMain(m *testing.M) {
 		fmt.Println(err)
 		os.Exit(1)
 	}
-	if testEnv.OSType != "linux" {
-		os.Exit(0)
-	}
 	err = environment.EnsureFrozenImagesLinux(testEnv)
 	if err != nil {
 		fmt.Println(err)