Also tried:

# Install yum-utils for yum-config-manager
RUN yum install -y yum-utils && yum clean all

# Add libreoffice repository and install
RUN yum-config-manager --add-repo http://download.opensuse.org/repositories/LibreOffice:/7.0/CentOS_7/ && \
    rpm --import http://download.opensuse.org/repositories/LibreOffice:/7.0/CentOS_7/repodata/repomd.xml.key && \
    yum install -y libreoffice && yum clean all