Added values only to discovery count.

[hoper-38709]

Add values only option to return from a DiscoveryLogic/ DiscoveryIterator.

[hlgp]

New direction: Turns out we don't need to aggregate the vis. We only need to return the first instance of each unique rowid.

So, if valuesOnly, break when you get the first valid TermEntry. Each next iteration will have just a single DiscoveredThing. Do the logic to only set the term and vis.

In setTop, precedent is already set to modify the column family to advance to the next column family. In the values only case we will want to skip to the next row. Note: appending a null byte to the end of the current row won't work, so recommend the next start key in the skip logic be the row and last possible column family (something like \uffff)