webadmin: custom preview dialog - close on success

Custom preview dialog:
close dialog only on return value success;
i.e. keep dialog open after canDoAction popup
(to allow selection amend).

Change-Id: I7c35c03bd1fdd7b8b2a46c7ff7596d344ab729e0
Bug-Url: https://bugzilla.redhat.com/1102783
Signed-off-by: Daniel Erez <derez@redhat.com>