The latter error indicates that librosa is not installed (or not in your python path). Did you see that message after installing with pip, or after cloning the repo?
In general, I recommend sticking to the pip install rather than cloning, unless you plan to do active development on the code (or need the latest development snapshot for some reason).
The first message (samplerate) is a warning, not an error. Everything will work properly, but certain operations -- resampling, CQT, time stretching and pitch shifting -- will not be as fast as they could be. To fix it, you need to install
libsamplerate (also available in debian/ubuntu via apt-get), and then install scikits.samplerate from pip.