webadmin,userportal: added singular form of nics assignment message

If there is only one nic, the message should be in singular

Change-Id: I312f8b9fb4808edf90492461b69541038af30393
Bug-Url: https://bugzilla.redhat.com/987858
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>