Add --keep-going mode to all.sh. In this mode, if a test fails, keep
running the subsequent tests. If a build fails, skip any tests of this
build and move on to the next tests. Errors in infrastructure, such as
git or cmake runs, remain fatal. Print an error summary at the end of
the run, and return a nonzero code if there was any failure.
In known terminal types, use color to highlight errors.
On a fatal signal, interrupt the run and report the errors so far.