Current osbuild will always print some non output even
when run with `--monitor=JSONSeqMonitor` because of the
unconditional `print/sys.stdout.write()` in `main_cli.py`.
This commit adds a new `-q` option to silence this so that something
like osbuild-composer can run `osbuild -q --monitor=JSONSeqMonitor`
to get pure json-seq output during the build.
The use-case is to run `osbuild --monitor-fd` from e.g. bib and
osbuild-composer so that we get pure json from the monitor-fd
and anything that goes on std{out,err} can be logged as it is
most likely error output.
ea14713f3a