core: TestStateAddModule old-style output
core: TestStateAddModule old-style output

Although the AddModule method now takes a new-style
module address as an argument, internally we're still
shimming it to a []string.

Therefore this test needs to still expect [][]string as
a result, rather tan []addrs.ModuleInstance.

hashicorp/terraform-plugin-sdk,hashicorp/terraform-plugin-sdk