Secondary ploop disk does not auto-mount during CT start.
Problem can be observed on containers based on Fedora 21 EZ templates.
This happens due to incorrect processing of file
systemd-fstab-generator (systemd component) inside the container.
The patch that solves this problem already exists in
systemd mainstream code
This fix is expected to be adopted in the upcoming updates of
systemd of Fedora 21.
Until the issue is fixed, as a workaround it is possible to mount the secondary ploop disk inside the contaier manually, by running "mount -a" inside CT after it`s start.