You may be better off with the RHEL / CentOS 7.1 libguestfs packages
which are available as a preview.  This is a substantial rebase with
many more features and somewhat faster too.  Follow the instructions here:
https://www.redhat.com/archives/libguestfs/2014-May/msg00090.html
Rich.
-- 
Richard Jones, Virtualization Group, Red Hat 
http://people.redhat.com/~rjones
Read my programming and virtualization blog: 
http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/