runs fail if hd5 files already exist

[karllark]

Currently runs fails if some of the intermediate hd5 files exist in the output directory. The workaround is to delete these files before each run (or the entire output directory). This is clearly not good. Better if the code detected the files that will cause a failure and removed them before trying to write them.

See BEAST-fitting/beast-examples#3

[s-goldman]

Should be fixed with beast-examples PR 15