The EPEL 7 SRPM for dragonegg https://dl.fedoraproject.org/pub/epel/7/SRPMS/d/dragonegg-3.4-4.el7.src.rpm contains CPU architecture specific code and therefore cannot be built on Mock on s390x. s390x needs to be listed in "ExcludeArch" in spec file.
Same for aarch64; this should probably be ExclusiveArch whichever architectures it actually works on.
dragonegg-3.4-5.el7 has been submitted as an update to Fedora EPEL 7. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2015-a6569ea17b
dragonegg-3.4-5.el7 has been pushed to the Fedora EPEL 7 stable repository. If problems still persist, please make note of it in this bug report.