Adds support for attaching GCEPersitentDisks

Adds GCEPersistentDisk volume struct
Adds gce-utils to attach disk to kubelet's VM.
Updates config to give compute-rw to every minion.
Adds GCEPersistentDisk to API
Adds ability to mount attached disks
Generalizes PD and adds tests.
PD now uses an pluggable API interface.
Unit Tests more cleanly separates TearDown and SetUp
Modify boilerplate hook to omit build tags
Adds Mounter interface; mount is now built by OS
TearDown() for PD now detaches disk on final refcount
Un-generalized PD; GCE calls moved to cloudprovider

Address comments.

pkg/volume/gce_util_test.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 volume
+
+import (
+	"testing"
+)
+
+func TestGetDeviceName(t *testing.T) {
+	tests := []struct {
+		deviceName    string
+		canonicalName string
+		expectedName  string
+		expectError   bool
+	}{
+		{
+			deviceName:    "/dev/google-sd0-part0",
+			canonicalName: "/dev/google/sd0P1",
+			expectedName:  "sd0",
+		},
+		{
+			canonicalName: "0123456",
+			expectError:   true,
+		},
+	}
+	for _, test := range tests {
+		name, err := getDeviceName(test.deviceName, test.canonicalName)
+		if test.expectError {
+			if err == nil {
+				t.Error("unexpected non-error")
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+		if name != test.expectedName {
+			t.Errorf("expected: %s, got %s", test.expectedName, name)
+		}
+	}
+}