Some generated module dirs don't work with new-style entrypoints

[lkubb]

For new-style entrypoints with only the root module referenced, the Salt loader tries to discover if the loaded root module contains submodules of a requested type by checking for </path/to/root_module>/<ext_type>. ext_type is passed in by the corresponding loader function and is not standardized regarding singular/plural. create-salt-extension only accounts for the sdb singular case, not the 12 (13*) other ones:

• auth
• cache
• metaproxy
• netapi
• output
• pillar
• pkgdb
• proxy
• roster
• sdb
• thorium
• wheel
• wrapper

Also, the generated directory for render is renders, but should be renderers to work.

* The 13th case is fileserver, which is not part of this generator. Is there any reason this was left out?