Valiadation of the configuration objects

[gtorodelvalle]

Currently, no validation is applied to the object passed as a configuration. See https://github.com/telefonicaid/iotagent-node-lib/blob/develop/lib/commonConfig.js#L157
This may cause problems in case the users of this module pass malformed-configurations.
Validating that the provided configuration is a valid one is needed.
This should be also implemented at a concrete agents level in case they also take configuration objects.