backport: stein, rocky
The reason it did not work before was that the other handlers had never been called
after [0], tasks from start.yml were move to handler which cannot act
like tasks, also bootstrap tasks must run after 'Restart mongodb container'.
This commit adds a notify after 'Restart mongodb container' for triger
task 'bootstrap_cluster.yml'.
[0] 40b635b9c5
Change-Id: I4e2fbe9a8f20afcc4e25a01e23e5231e74eeeec4
6bb01bd7b1