Fix additional issues related to BOM file generation

Avoid using set bash builtin for setting error on pipes

Since set is not available in the docker image avoid using it and instead change the piped commands to be run independently.

generate_bom.py: Only parse bin2sources files

During the process of building the BOM file the output of dh_dwarf2sources is parsed to get the list of files used to build the binary. In order to do that the script scans for json files on the doc folder, however since some packages ship json files this leads to errors.

Fix this by only taking into account files generated by dh_dwarf2sources which end in "_bin2sources.json".