Graph blobs for Code shows incorrect "label"

[CasperWA]

Found out through @mbercx's online offline show-and-tell for the new basic tutorial.

When he created a new Code labelled add@<COMPUTER>, the Code showed up the subsequently generated graphs as bash@<COMPUTER>. This is confusing.

[giovannipizzi]

Here is the line to fix:

aiida-core/aiida/tools/visualization/graph.py

Line 210 in 6220e85

sublabel = '{}@{}'.format(os.path.basename(node.get_execname()), node.get_computer_name())

In general, should we use node.get_description() that was designed exactly to provide a short textual description? And possibly adapt that method to return something we like?