The RPM for RHEL7 (and other distros that use systemd) should execute systemctl daemon-reload after updating the RPM, to prevent this error message:
Warning: mariadb.service changed on disk. Run 'systemctl daemon-reload' to reload units.
This should occur in the %post-install section, otherwise changes to the systemd unit will not get picked up until a manual intervention is made.
Not sure if related, but after updating the RPM, systemd seems to lose control of the running daemon, but I'll log this as a separate issue.