Feature/filestorage availabilityzones list (#153)

* sfs: Add support for Availability Zone List

* sfs: Add acceptance tests for Availability zones List

* sfs: Fix review comments
diff --git a/openstack/sharedfilesystems/v2/availabilityzones/urls.go b/openstack/sharedfilesystems/v2/availabilityzones/urls.go
new file mode 100644
index 0000000..fb4cdcf
--- /dev/null
+++ b/openstack/sharedfilesystems/v2/availabilityzones/urls.go
@@ -0,0 +1,7 @@
+package availabilityzones
+
+import "github.com/gophercloud/gophercloud"
+
+func listURL(c *gophercloud.ServiceClient) string {
+	return c.ServiceURL("os-availability-zone")
+}