Fix metrics filter with colon : in query value

Example of a metric filter affected by this:
```
cloudsql.googleapis.com/database:resource.labels.database_id=project-id:database-name
```

Signed-off-by: Daniel Kontsek <[email protected]>

Author: dn0

utils/utils.go

@@ -46,7 +46,7 @@ func SplitExtraFilter(extraFilter string, separator string) (string, string) {
 	if mPrefix[0] == extraFilter {
 		return "", ""
 	}
-	return mPrefix[0], strings.Join(mPrefix[1:], "")
+	return mPrefix[0], strings.Join(mPrefix[1:], separator)
 }
 
 func ProjectResource(projectID string) string {

utils/utils_test.go

@@ -31,3 +31,11 @@ var _ = Describe("ProjectResource", func() {
 		Expect(ProjectResource("fake-project-1")).To(Equal("projects/fake-project-1"))
 	})
 })
+
+var _ = Describe("SplitExtraFilter", func() {
+	It("returns a metric prefix and filter query", func() {
+		metricPrefix, filterQuery := SplitExtraFilter("This_is__a-MetricName.Example/with:filter.name=filter:value", ":")
+		Expect(metricPrefix).To(Equal("This_is__a-MetricName.Example/with"))
+		Expect(filterQuery).To(Equal("filter.name=filter:value"))
+	})
+})