Whether the read test after writing was done on the same node was
random for drivers that weren't locked onto a single node. Now it is
deterministic: it always happens on the same node.

The case with reading on another node is covered separately for test
configurations that support it (not locked onto a single node, more
than one node in the test cluster).

As before, the TestConfig.ClientNodeSelector is ignored by the
provisioning testsuite.