fix(disk_util): Install syslinux with extlinux
fix(disk_util): Install syslinux with extlinux

Attempting to work around an apparent race in mtools, the command
'extlinux' these days is just the install tool for mounted partitions
while 'syslinux' is for unmounted devices.

trnubo/scripts,smilart/scripts,smilart/scripts,mischief/scripts,mjg59/scripts,vmware/coreos-scripts,fivethreeo/scripts,vmware/coreos-scripts,zhang0137/scripts,endocode/scripts,mjg59/scripts,nicescale/scripts,coreos/scripts,mischief/scripts,andrejro/coreos--scripts,endocode/scripts,sigma/coreos-scripts,zhang0137/scripts,sigma/coreos-scripts,nicescale/scripts,endocode/scripts,gtank/scripts,andrejro/coreos--scripts,coreos/scripts,marineam/coreos-scripts,fivethreeo/scripts,BugRoger/scripts,marineam/coreos-scripts,BugRoger/scripts,mjg59/scripts,trnubo/scripts,glevand/coreos--scripts,fivethreeo/scripts,sigma/coreos-scripts,nicescale/scripts,mischief/scripts,zhang0137/scripts,smilart/scripts,andrejro/coreos--scripts,vmware/coreos-scripts,gtank/scripts,gtank/scripts,trnubo/scripts,marineam/coreos-scripts,BugRoger/scripts,glevand/coreos--scripts