webadmin: fixed edit name availability in tree context

When a specific item (for example, an actual host -- not
"Hosts") is selected in the left-pane tree, we need to
disable editing the name of that item.

Change-Id: Ie50a6fcfeacdc94fe900f6569180106c31f5e9c8
Bug-Url: https://bugzilla.redhat.com/858952
Signed-off-by: Greg Sheremeta <gshereme@redhat.com>