iotests.py: Add node_info()

This function queries a node; since we cannot do that right now, it
executes query-named-block-nodes and returns the matching node's object.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20190201192935.18394-8-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/iotests.py

@@ -543,6 +543,13 @@ class VM(qtest.QEMUQtestMachine):
                 else:
                     iotests.log(ev)
 
+    def node_info(self, node_name):
+        nodes = self.qmp('query-named-block-nodes')
+        for x in nodes['return']:
+            if x['node-name'] == node_name:
+                return x
+        return None
+
 
 index_re = re.compile(r'([^\[]+)\[([^\]]+)\]')