webadmin: Limiting vnic name label width on vm dialog

LabelWithTooltip is used to limit the width of the vnic name
label.
In case the name width is bigger than the limited width (in
pixels), the name is trimmed and '...' are add to it.
The tooltip displays the whole name.

Change-Id: I32d30aa8d1824b127030a533fcde57aaa75983b3
Bug-Url: https://bugzilla.redhat.com/1029973
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>