Add try/except around submit() to handle failures

[will-moore]

Fixes #11.

This first commit does the minimum requested by @pwalczysko of simply not failing if the DiskUsage submit failed.

Happy to also add an option to specify the timeout as suggested by @joshmoore.
But just wondering what the 500 loops means at https://github.com/ome/omero-demo-cleanup/blob/main/src/omero_demo_cleanup/library.py#L118 ?

Is that 500 pings to wait for a result - and how long between each one?
E.g. If a user were to enter their own value, would this look like a --loops parameter? Would anyone know what that means? Or would we go for --seconds parameter for how long to wait? And how does this map to loops?

[jburel]

@will-moore could you fix the flake8 issue?