webadmin: Add/Remove VNICs in Add/Edit VM dialog

Enabled adding/removing VNICs in the VM dialogs using
AddRemoveRowWidget.

Change-Id: Id7654d137541aec64ce19aa309021b307253171e
Bug-Url: https://bugzilla.redhat.com/1003779
Signed-off-by: Lior Vernia <lvernia@redhat.com>