Style changes and cleanup

This patch makes stylistic changes to error strings, unexports method names by lower casing them, removes unused dataSetMetric, and adds copyright/licence information.

Signed-Off-By: Corey Stewart <stewa169@purdue.edu>

collector/zfs_linux_test.go

@@ -1,3 +1,16 @@
+// Copyright 2016 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package collector
 
 import (
@@ -6,7 +19,6 @@ import (
 )
 
 func TestArcstatsParsing(t *testing.T) {
-
 	arcstatsFile, err := os.Open("fixtures/proc/spl/kstat/zfs/arcstats")
 	if err != nil {
 		t.Fatal(err)
@@ -40,5 +52,4 @@ func TestArcstatsParsing(t *testing.T) {
 	if !handlerCalled {
 		t.Fatal("Arcstats parsing handler was not called for some expected sysctls")
 	}
-
 }