grub2-client.xml node file expects access to command /opt/rocks/sbin/modify-grub2 to modify bootflags of installing node.
/opt/rocks/sbin/modify-grub2 is provided by rocks-admin RPM from Rocks core roll.
rocks-admin RPM is not added to updates.img by build-updates-img.py in Rocks base roll and therefore is not available during node install.