I think these fonts should be installed automatically together with other fonts.
Added as default package to @fonts group.

     <packagereq type="default">open-sans-fonts</packagereq>

# find -name "open-sans-fonts*" | sort
./Client/source/tree/Packages/open-sans-fonts-1.10-1.el7.src.rpm
./Client/x86_64/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm
./ComputeNode/source/tree/Packages/open-sans-fonts-1.10-1.el7.src.rpm
./ComputeNode/x86_64/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm
./Server/ppc64/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm
./Server/s390x/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm
./Server/source/tree/Packages/open-sans-fonts-1.10-1.el7.src.rpm
./Server/x86_64/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm
./Workstation/source/tree/Packages/open-sans-fonts-1.10-1.el7.src.rpm
./Workstation/x86_64/os/Packages/open-sans-fonts-1.10-1.el7.noarch.rpm

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHEA-2015-0524.html