SchedulerStateRest.getLiveLogFromJob method does not work properly

[Mykhailenko]

We had an issue with scheduling-system-tests: src/test/java/org/ow2/proactive/systemtests/test/rest/scheduler/node/task/termination/NodeTaskTerminationSigtermTest.java test (workaround in this commit).
It happened because job was not running yet and we started to use

dockerSystemTestRestJobHelper.getLiveLogFromJob

method to get LiveLog from the job. And this LiveLog was always empty. But if you wait until job is already running, than getLiveLogFromJob method works properly.