remove all uses of a bare "except:" clause

[mhl]

There are 12 places in the codebase where there is a bare except: - this is bad practice, as explained here:

• https://docs.python.org/2/howto/doanddont.html#except

In some cases, we might want to remove the exception handling completely, and then add back the handling for selected exception types as the exceptions are raised. In others, it will be immediately clear from examining the code which exception was intended to be caught.