Remove the complex and unreliable code which inferred the node name
hierarchy only from data returned by 'query-named-block-nodes'. It turns
out that query-blockstats contain the full hierarchy of nodes as
perceived by qemu so the inference code is not necessary.

In query blockstats, the 'parent' object corresponds to the storage
behind a storage volume and 'backing' corresponds to the lower level of
backing chain. Since all have node names this data can be really easily
used to detect node names.

In addition to the code refactoring the one remaining test case needed
to be fixed along.
Reviewed-by: NEric Blake <eblake@redhat.com>

Rename 'json' and related variables to 'nodeNameJson'. Also rename the
test files along. This is a preparation for modifying how we detect node
names which will also require data from 'query-blockstats'.
Reviewed-by: NEric Blake <eblake@redhat.com>

Test cases named '1' and '2' differed only in the length of the backing
chain, so remove test case '2' and rename test '1' to 'basic'.
Reviewed-by: NEric Blake <eblake@redhat.com>

The code is rather magic so a test case will help making sure that
everything works well. The first case is a simple backing chain.