Raise CollectError when Prometheus query returns an error

As described in the Prometheus HTTP API documentation [1], the JSON
response to a Prometheus query includes a status field, which was
ignored by CloudKitty. If it is set to "error", raise a CollectError
exception to log the error type and details.

For example, a query with a metric name containing a dot will produce
the following error:

    cloudkitty.collector.exceptions.CollectError: bad_data: invalid parameter "query": 1:25: parse error: unexpected character: '.'

[1] https://prometheus.io/docs/prometheus/latest/querying/api/

Change-Id: I0c2892a39ec50163de251b38d34493db6a22c858
Story: 2009869
Task: 44564

cloudkitty/collector/prometheus.py

@@ -219,6 +219,11 @@ class PrometheusCollector(collector.BaseCollector):
         except PrometheusResponseError as e:
             raise CollectError(*e.args)
 
+        if res['status'] == 'error':
+            error_type = res['errorType']
+            error_msg = res['error']
+            raise CollectError("%s: %s" % (error_type, error_msg))
+
         # If the query returns an empty dataset,
         # return an empty list
         if not res['data']['result']:

releasenotes/notes/prometheus-error-8eab9f1793c2280c.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Raises a ``CollectError`` exception with error details when a Prometheus
+    query returns an error status.