webadmin: ENTER does not execute default command

Pressing the enter key does not execute the
default command for all models that extend
SearchableListModel

Change-Id: I4ebfa08d2d3bcd0d2089febbe19e54c76cef25ec
Bug-Url: https://bugzilla.redhat.com/1126324
Signed-off-by: Ravi Nori <rnori@redhat.com>