AssertSpreadAcrossNodes and CountInstancesPerNode lost their only caller when
the instance-distribution test was removed. Beyond being dead, the assertion
helper documented minNodes=1 as an acceptable logging-only mode inherited from
the bash driver, which is the pattern that let a placement test pass while
every instance landed on one node.
InstanceHostingNode and its ps helpers stay; five multinode tests use them.
joshsiv-mulga
b579ebe1a2