Support disabling NFSv2, NFSv3 in (redhat) /etc/sysconfig/nfs

[bschonec]

Add the ability to turn off NFS v2 and v3 via the (rhel variants) /etc/sysconfig/nfs file: From Red Hat documentation:

Procedure 8.2. Configuring an NFSv4-only Server

To configure your NFS server to support only NFS version 4.0 and later:
Disable NFSv2, NFSv3, and UDP by adding the following line to the /etc/sysconfig/nfs configuration file:
RPCNFSDARGS="-N 2 -N 3 -U"