sleep a bit after starting a node and before asserting how many nodes ar...

...e running

based on

http://172.19.49.85/view/arakoon-git/job/arakoon-amplidata-git-system-tests-slow-RIGHT/lastCompletedBuild/testReport/arakoon_system_tests.server.right/system_tests_learner/test_learner/
http://10.101.186.8/jenkins/jobs/jenkins-arakoon-amplidata-git-system-tests-slow-RIGHT-9/home/jenkinslxc/qbase3/var/tmp/arakoon_system_tests/test_learner/sturdy_2/log/