nfs-utils: bump to version 1.2.6

Bump nfs-utils to version 1.2.6
Portmap or rpcbind (which we don't have) is required so select it.
Remove nfsiostat if there's no target python.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>