Fixed nova command to get available flavors

The nova command for getting the flavors is not
nova list-flavors
but
nova flavor-list

contrib/terraform/openstack/README.md

@@ -86,7 +86,7 @@ This will provision one VM as master using a floating ip, two additional masters
 Additionally, now the terraform based installation supports provisioning of a GlusterFS shared file system based on a separate set of VMs, running either a Debian or RedHat based set of VMs. To enable this, you need to add to your `my-terraform-vars.tfvars` the following variables:
 
 ```
-# Flavour depends on your openstack installation, you can get available flavours through `nova list-flavors`
+# Flavour depends on your openstack installation, you can get available flavours through `nova flavor-list`
 flavor_gfs_node = "af659280-5b8a-42b5-8865-a703775911da"
 # This is the name of an image already available in your openstack installation.
 image_gfs = "Ubuntu 15.10"