Upgrader should check for tools before downloading

[John A Meinel]

When we moved the Upgrader over to the API we lost the check if the tools already existed in the target.

In 1.16 when Upgrader sees that an Upgrade is needed, it *always* downloads the tools, extracts them, and only after doing all that work does it notice that the tools already exist.

The old Upgrader code had a check just before download if the target tools could be read already. Arguably we could check before we download, and then one more time between downloading the tools and actually extracting them (since it takes time to actually do the download).