engine : execute flag should set when no exception occurs

setCommandExecuted should be called only when  no
exceptions are thrown during the command execution

Change-Id: I090fec2f55893c799164e01ec36c727c8244cab4
Bug-Url: https://bugzilla.redhat.com/1129885
Signed-off-by: Ravi Nori <rnori@redhat.com>