Don't install syslinux-nonlinux on rhel7
Don't install syslinux-nonlinux on rhel7

the syslinux tools are in the syslinux package on
rhel7 and friends, but in rhel8 have moved to
syslinux-nonlinux

Change-Id: Iea74c2be6fbd738f35f178fa189384dd37579277

openstack/ironic,openstack/ironic