Use the new recipe parser from the BuildInfo module, add a
getbuildinfo_post_common function instead of calling
getbuildinfo_post with a patched cgi hash.

This allows the user to pass a recipe file or a cpio archive
with files of the package.

jsc#OBS-352

Also move the _service file parsing into the sourceinfo_parse()
function.

No need to hop through the Digest module.

This is similar to what we do for Docker/Kiwi.

This commit also improves the patchinfo detection, as we do
not have package information for locked patchinfos. So we
just check if there is an "updateinfo.xml" in the bininfo
of the packages.