Catch flush issues when a logger is closed

[coreyeng]

If using multiple shells in the same workspace, there's chance logger files will step on each other, particularly last, and particularly noticeable with simulations. This will generate an exception, but doesn't affect a single pattern. However, this will kill a flow simulation prematurely if it occurs.

This is a quick fix to just catch any errors flushing to a log file and print them to the user, without propagating the exception.

For example, instead of seeing this:

You'll see:

Note the warnings here - just saying stale log file, which is expected, but now results in the warning instead of an exception.

[coreyeng]

Released 0.60.12 with this merged.