Fix termination condition for st2 execution tail CLI command.
Fix termination condition for st2 execution tail CLI command.

StackStorm/st2,Plexxi/st2,nzlosh/st2,StackStorm/st2,nzlosh/st2,Plexxi/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,StackStorm/st2,Plexxi/st2,nzlosh/st2