Add e2e test for multiple metric not found errors

Author: teqwve

cmd/mockbackend/testcases/i844/i844.yaml

@@ -0,0 +1,34 @@
+version: "v1"
+test:
+    apps:
+        - name: "carbonapi"
+          binary: "./carbonapi"
+          args:
+              - "-config"
+              - "./cmd/mockbackend/carbonapi_singlebackend.yaml"
+              - "-exact-config"
+    queries:
+            - endpoint: "http://127.0.0.1:8081"
+              delay: 1
+              type: "GET"
+              URL: "/render?format=json&target=maxSeries(group(some.existing.metric.*, some.nonexisting.metric.*))&target=minSeries(group(some.existing.metric.*, other.nonexisting.metric.*))"
+              expectedResponse:
+                  httpCode: 200
+                  contentType: "application/json"
+                  expectedResults:
+                          - metrics:
+                                  - target: "maxSeries(group(some.existing.metric.*, some.nonexisting.metric.*))"
+                                    datapoints: [[3.0, 1],[3.0, 2],[3.0, 3]]
+                                  - target: "minSeries(group(some.existing.metric.*, other.nonexisting.metric.*))"
+                                    datapoints: [[1.0, 1],[1.0, 2],[1.0, 3]]
+
+listeners:
+        - address: ":9070"
+          expressions:
+                     "some.existing.metric.*":
+                         pathExpression: "some.existing.metric.*"
+                         data:
+                             - metricName: "some.existing.metric.a"
+                               values: [1.0, 1.0, 1.0]
+                             - metricName: "some.existing.metric.b"
+                               values: [3.0, 3.0, 3.0]