Right now, they appear on screen when using --details-to-stdout. This
does not work well with Travis CI and screws up the log.
Disabling the progress bars in abuild works just like Alpine does it in
their Travis CI script: Exporting SUDO_APK as
"abuild-apk --no-progress" instead of "abuild-apk".
test_check_checksums.py: Run "pmbootstrap build_init" before building
any packages, so it is a bit less verbose (downloading the APKINDEX
files etc.). Later we run the build init code again (because we use
--strict while building the packages), but then the APKINDEX files
are already present. So overall the log is a bit shorter before the
building starts. (It is still logged to the logfile, which gets
printed on error anyway.)