minijasmine: Print test JS errors output if any
JS errors on tests are currently only visible by checking the log files, and this can make debugging annoying.
So, save error output in a global jasmine array and print it in case we got errors.
In theory this could be just made easier by only using printerr (without # prefix) on specDone, as meson's tap parser doesn't look at stderr.
However, I liked the idea of having some different context so that we can print them differently depending on the environment (including test name or separating them by lines for easier reading).