Properly surface errors from build commands

the commit 38b13a3 ("Use asyncio for subprocess calls") broke the way
exit codes are reported from the podman compose build command.

The tasks are awaited as they finish which means that if a later build
finishes sucessfully after a failing build, it overwrites status.

Previously the `parse_return_code` function would skip updating the status
if the new return code was zero, but in removing it, this logic was not
carried forward.

Fixes: 38b13a3 ("Use asyncio for subprocess calls")

Author: charliemirabile

podman_compose.py

@@ -2613,7 +2613,7 @@ async def compose_build(compose, args):
     status = 0
     for t in asyncio.as_completed(tasks):
         s = await t
-        if s is not None:
+        if s is not None and s != 0:
             status = s
 
     return status