Problem description:
It is not possible to NFS mount /usr exported from another
machine, because /etc/rc.d/init.d/network uses the command
/usr/bin/xargs which is not present at that time.

Quick solution:
Copy /usr/bin/xargs to /bin/xargs.

Proper solution:
Do not use /usr/bin/xargs in /etc/rc.d/init.d/network, but
use $() from bash instead. Generally do not use ANY file
from /usr before mounting NFS volumes and after unmounting
NFS volumes.