Add install_nodejs and install_npm functions
Add install_nodejs and install_npm functions

According to the documentation[1], it's necessary to install nodejs
and npm tools for DCAE and other projects. This change only adds the
specific functions to the library for future references.

[1] https://wiki.onap.org/display/DW/Setting+Up+Your+Development+Environment#SettingUpYourDevelopmentEnvironment-InstallNodeJS

electrocucaracha/vagrant-onap