Added contrail::system_config, added unit tests

contrail::system_config configure the basic system parameters to
make the system ready to run contrail control node applications in it.

Also enabled rspec, added unit tests for contrail::system_config
this is a potential behavior change b/c it assumes that you always want to update /etc/hosts with whatever is listed as the first interfaces ip address. I don't know enough about the requirement here to know if that is sufficient, I'm just noting that it's a behavior change.