Problem
--------

When a data node is restarted, the node is first stopped and after
a fixed wait, it is assumed to have entered the NOT_STARTED state.
At this point, a start signal is fired. If the node is not ready
i.e. has not completed stopping during the wait and is therefore
not in the NOT_STARTED state, the start signal is silently ignored
leaving no error even though the restart process is incomplete.

Fix:
----

Check if the data node has reached the NOT_STARTED state before
the start signal is fired. The wait for the node to reach this
state is split into 2 separate checks:

1. Wait for the data node(s) to start shutting down
2. Wait for the data node(s) to complete shutting down and reach
   NOT_STARTED state

In the event of either of these cases timing-out, the restart is
considered to have failed and an error message is returned.