Improve exception from Store.failIfCorrupted

[rmuir]

If you have previously corrupted files, this method currently builds an exception like:

failed engine [corrupted preexisting index]
failed to start shard

Followed by a CorruptIndexException:

builder.append(" Corrupted index [");
builder.append(file).append("] caused by: ");
builder.append(msg);
ex.add(new CorruptIndexException(builder.toString()));

Is it possible to improve this:

1. In the string we write (msg), can the string have more details when we write it, e.g. including full stracktrace?
2. can we change the text 'corrupted preexisting index' to either 'preexisting corrupted index' or 'index has preexisting corruption' or similar?

[s1monw]

I wonder if we should do both. And log the stacktrace as debug?

[clintongormley]

@rmuir are you taking this or should it be an adoptme?