Update : Just went onto a client NIS server that was running 14.10 and checked the /etc/default/nis file and it was set to master, upgraded to 15.04 and it was changed to NISSERVER=false and all clients couldn't bind.
Changed manually back to NISSERVER=master and all is OK.
Looks like the upgrade doesn't observe the original settings
Update : Just went onto a client NIS server that was running 14.10 and checked the /etc/default/nis file and it was set to master, upgraded to 15.04 and it was changed to NISSERVER=false and all clients couldn't bind.
Changed manually back to NISSERVER=master and all is OK.
Looks like the upgrade doesn't observe the original settings