When running git cl presubmit --all  which is handy for finding
latent presubmit bugs, the 'No diff found for %s' gets printed many
thousands of times, making actual issues difficult to find. This change
suppresses that message, to make actual issues easier to find.

The message for slow presubmits prints the name of the slow presubmit,
but there are 243 different CheckChangeOnCommit functions, so the name
is actually not sufficient. Therefore this change plumbs through the
path to the script containing the presubmit and prints it.

Similarly, the cpplint message "Done processing %s" doesn't add enough
value.

These changes will make it easier to find the signal in the presubmit
noise.

Bug: 1309977
Change-Id: Iba40b5748266e3296eeb530bb00182db4814aa5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3556594Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>