backend: correctly obtain information about a publication

The previous code "worked" only by an accident. Previously we called
the publication endpoint without a trailing slash (changed in d8013c),
which caused some weird redirect and returned a list of all
publications, not the one created publication that I expected.

We need to manually query the publication href from the submitted
task.

backend/copr_backend/pulp.py

@@ -105,6 +105,12 @@ def get_distribution(self, name):
         url += self._urlencode({"name": name, "offset": 0, "limit": 1})
         return requests.get(url, **self.request_params)
 
+    def get_task(self, task):
+        """
+        Get a detailed information about a task
+        """
+        url = self.config["base_url"] + task
+        return requests.get(url, **self.request_params)
     def _urlencode(self, query):
         """
         Join a dict into URL query string but don't encode special characters

backend/copr_backend/storage.py

@@ -189,7 +189,14 @@ def publish_repository(self, chroot, **kwargs):
                            repository, response.text)
             return False
 
-        publication = response.json()["results"][0]["pulp_href"]
+        task = response.json()["task"]
+        response = self.client.get_task(task)
+        if not response.ok:
+            self.log.error("Failed to get Pulp task %s because of %s",
+                           task, response.text)
+            return False
+
+        publication = response.json()["created_resources"][0]
         distribution_name = self._distribution_name(chroot)
         distribution = self._get_distribution(chroot)