Fix for flaky excel tests

Upon checking if an instance of Excel is already running, using `Marshal.GetActiveObject`, a FileNotFoundException occurs sometimes with 'DynamoCore.XmlSerializers` which is not clear why. This exception also makes Excel tests very flaky. It is found that just swallowing these exceptions and creating a new excel instance below causes the test to continue and successfuly pass. 

I am therefore changing the catch block to catch generic exceptions of type `Exception` for this fix.