Improve error handling for Koji

Avoid printing stack trace on Koji XMLRPC faults. Log the error and pass
it to the client instead.

JIRA: RHELWF-10505, RHELWF-10400

greenwave/resources.py

@@ -204,7 +204,14 @@ def retrieve_koji_build_target(task_id, koji_url: str):
 def _retrieve_koji_build_attributes(nvr: str, koji_url: str):
     log.debug('Getting Koji build %r', nvr)
     proxy = _koji(koji_url)
-    build = proxy.getBuild(nvr)
+
+    try:
+        build = proxy.getBuild(nvr)
+    except xmlrpc_client.Fault as e:
+        error = f'Failed to get Koji build for "{nvr}": {e}'
+        log.debug(error)
+        raise BadGateway(error)
+
     if not build:
         raise NotFound(
             'Failed to find Koji build for "{}" at "{}"'.format(nvr, koji_url)