npm: change install directory to upstream default

npm: change install directory to upstream default

The node binary searches for packages in a number of locations, the last
of which is $PREFIX/lib/node (here: /usr/lib/node) from the list of
GLOBAL_FOLDERS [1]. So change the installation directory for all
packages depending on npm.bbclass to that location. This removes the
need to define the NODE_PATH variable to the non-standard
/usr/lib/node_modules value.

While the Tips for Package Managers [2] discusses installing packages to
/usr/lib/node_modules/<name>/<version>, this has several drawbacks:

 * it does not work for the REPL as mentioned in the documentation
 * it also does not work for any code _not_ installed as a global
   package under /usr/lib/node_modules (e.g. /usr/share/foo.js will not
   find any packages below /usr/lib)
 * using the non-default location and then having to set NODE_PATH
   barely saves any time: there are only two file-system lookups (to the
   legacy $HOME/.node_modules and $HOME/.node_libraries) directories
   before the library would be found

And the suggestion was made in the context of deduping the node_modules
tree by installing all packages in a flat hierarchy and using symlinks
to the correct version of each dependency. This is not what OpenEmbedded
does, so none of those benefits (deduping, cleaner packages) are being
had by shifting the installation directory to /usr/lib/node_modules.

The choice of a "proper" installation path is not helped by npm
installing to /usr/lib/node_modules if asked to install globally. Still,
using the location expected by nodejs (/usr/lib/node) seems the right
choice.

[1]: https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders
[2]: https://nodejs.org/api/modules.html#modules_addenda_package_manager_tips

(From OE-Core rev: c73bc49038effd64f2c2542c1f4da8b6a4168477)

Signed-off-by: Olaf Mandel <o.mandel@menlosystems.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>