autohelp: avoid help strings on multiple lines
autohelp: avoid help strings on multiple lines

Multiple lines means dealing with indentation, which is complicated and
not a problem for automatically generated tables. Use the same helptext
generation in autohelp than in extract_swift_flags.

Change-Id: Ibd64d3f0387c3e7f1f3aacf57be5f0c97addf5c9

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