tools/update-distro-hash: rename, fetch the repository if appropriate

tools/update-distro-hash: rename, fetch the repository if appropriate

Let's rename the tool to tools/fetch-distro. It's useful to be able to fetch
the distro directly. But when that functionality is added, the old name is
confusing.

Now --update/-u must be specified to update the commits.

--reference-if-able is used to speed up the clone of debian.
It saves about 75% of the download.

(cherry picked from commit 82c459f910c3036b22c9f41472b622ef4bfdab1d)