BUG: jira NETCONF-493 ReconnectPromise throws IllegalStateException continuously
ReconnectPromise will execute method setFailure() more than once
if reconnecting to a netconf device failed more than once, and the
setFailure() method will start throwing IllegalStateException at
the second time invocation, so there should add limitation to the
call of setFailure() to avoid IllegalStateException.
Change-Id: I2d6802e6ac643215192527319d565da36a16caf5
Signed-off-by: Li guosheng <li.guosheng6@zte.com.cn>