(#13379) Add path of pluginsync'd lenses to Augeas load_path automatically

The path $libdir/augeas/lenses is added to the Augeas load_path initialisation
option automatically to support lenses being pluginsynced. Lenses should be
added into the <module>/lib/augeas/lenses directory inside a module.

The load_path parameter has been expanded to support an array of paths as well
as a colon-separated list.