Change the fs_passno of nfs to 0

Change the fs_passno of nfs to 0

There is a bug that kdump-initrd contains entry requesting nfs dump
filesystem to get filesystemchecked. And there is an erro message said
that nfs need be checked. But there's no fsck for nfs utility, e.g
fsck.nfs like other file system. Whatever fs_passno 0 or 2 are passed,
no fsck is executed at all for nfs mount.But in dracut, set it to be 2
always, so the erro message appear and it should be set to 0.

In the fstab,the sixth variable fs_passno stands for that the device need
checked or not,and dracut set it to "2".To fix this issue, it should
be "0" when the device is nfs.The third variable stands for the type of
the filesystem and we can use it to judge whether the device is nfs.
So when the third variable of fstab contains "nfs", the sixth variable
fs_passno should be set to "0".

Signed-off-by: Chao Fan <cfan@redhat.com>