Iotagent plugins loaded by default or by config.js

[versatildefuy]

Hello guys,

as @AlvaroVega explains in telefonicaid/iotagent-node-lib#913 (comment) iotagent-node-lib plugins are not loaded in this iotagent.

It would be interesting to load the plugins in order to make use of this functionality from the docker images.

Thank you in advance