A note to my future self from the past version who wasted time on this for a 2nd time (filtering through the many google solutions before finding the one that worked):
This has happened some other time besides trying to install rbenv. Curl complains error setting certificate verify locations and a BUILD FAILED error ensues.
several potential fixes involved linking in various other paths, this is what worked for me:
sudo apt-get install ca-certificates
sudo mkdir -p /etc/pki/tls/certs
sudo ln -s /etc/ssl/certs/ca-certificates.crt /etc/pki/tls/certs/ca-bundle.crt
btw, this also fixes the issue with carina/rackspace setup