Application: add some comments

Signed-off-by: Tomas Hozza <thozza@redhat.com>
BuildHelper: log exit codes of buildtools if building failed

Signed-off-by: Tomas Hozza <thozza@redhat.com>
BuildHelper: rombuild: use output file instead of stdout

Signed-off-by: Tomas Hozza <thozza@redhat.com>