webadmin: Giving the option of whether to activate an imported domain

Added a checkbox in import storage domain popup which lets the user decide
whether the domain should be activated after the import, default is not to
activate

Change-Id: I14dbe9c41e1ff194ee8c1e03cd7ccff223ec14e1
Signed-off-by: Tal Nisan <tnisan@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1096971