FYI: This happened because katello-installer nightlies were failing.
foreman-installer and katello-installer get out of sync resulting in
broken caches. The workaround is to install yard and puppet-strings:
/opt/puppetlabs/puppet/bin/gem install yard
/opt/puppetlabs/puppet/bin/gem install puppet-s
Specifically, using koji repos in boxes.yaml:
cmd: foreman-installer -v --scenario "katello-devel"
--foreman-proxy-tftp=true --disable-system-checks
--katello-devel-github-username thomasmckay
start: 2017-05-05 19:52:26.544551
end: 2017-05-05 19:52:27.828586
delta: 0:00:01.284035
stderr: /usr/
