Fix oversight in patch 221559
Fix oversight in patch 221559

In patch 221559 with change id Ic3fc9ed5f3644497e4dd25a92ded01ee0224cdef,
a couple of calls to generate_subcommands() were not replaced with the
new method discover_and_generate_subcommands(). Fixing it in this patch.

Change-Id: I4f46d275a15685dc76e42b24b21b4930a94bc184

openstack/openstack-doc-tools,openstack/openstack-doc-tools