silent fail when sequence directory is read-only

[wwhsiao]

It appears that if the directory containing the sample sheet and the sequence data is read-only, the program (v2) will fail after the validation step without any error or warning messages. Presumably this is because it can not create the .miseqUploaderInfo file and is waiting to do so. It'll be useful to have an error message when this occurs rather than a silent fail.

[apetkau]

Thanks for reporting this. There's a few other improvements we want to make to the error messages as well.