stackdriver: test that no interpolation is done when there are no wildcards

(cherry picked from commit 5f7795aa1f)

pkg/tsdb/stackdriver/stackdriver_test.go

@@ -440,7 +440,13 @@ func TestStackdriver(t *testing.T) {
 				value := interpolateFilterWildcards("us-ce*tral1-*")
 				So(value, ShouldEqual, `monitoring.regex.full_match("^us\\-ce.*tral1\\-.*$")`)
 			})
+
+			Convey("and no wildcard is used", func() {
+				value := interpolateFilterWildcards("us-central1-a}")
+				So(value, ShouldEqual, `us-central1-a}`)
+			})
 		})
+
 	})
 }