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/api/types.go

@@ -92,6 +92,9 @@ type VolumeSource struct {
 	HostDir *HostDir `yaml:"hostDir" json:"hostDir"`
 	// EmptyDir represents a temporary directory that shares a pod's lifetime.
 	EmptyDir *EmptyDir `yaml:"emptyDir" json:"emptyDir"`
+	// GCEPersistentDisk represents a GCE Disk resource that is attached to a
+	// kubelet's host machine and then exposed to the pod.
+	GCEPersistentDisk *GCEPersistentDisk `yaml:"persistentDisk" json:"persistentDisk"`
 }
 
 // HostDir represents bare host directory volume.
@@ -111,7 +114,28 @@ const (
 	ProtocolUDP Protocol = "UDP"
 )
 
-// Port represents a network port in a single container.
+// GCEPersistent Disk resource.
+// A GCE PD must exist and be formatted before mounting to a container.
+// The disk must also be in the same GCE project and zone as the kubelet.
+// A GCE PD can only be mounted as read/write once.
+type GCEPersistentDisk struct {
+	// Unique name of the PD resource. Used to identify the disk in GCE
+	PDName string `yaml:"pdName" json:"pdName"`
+	// Required: Filesystem type to mount.
+	// Must be a filesystem type supported by the host operating system.
+	// Ex. "ext4", "xfs", "ntfs"
+	// TODO: how do we prevent errors in the filesystem from compromising the machine
+	FSType string `yaml:"fsType,omitempty" json:"fsType,omitempty"`
+	// Optional: Partition on the disk to mount.
+	// If omitted, kubelet will attempt to mount the device name.
+	// Ex. For /dev/sda1, this field is "1", for /dev/sda, this field is 0 or empty.
+	Partition int `yaml:"partition,omitempty" json:"partition,omitempty"`
+	// Optional: Defaults to false (read/write). ReadOnly here will force
+	// the ReadOnly setting in VolumeMounts.
+	ReadOnly bool `yaml:"readOnly,omitempty" json:"readOnly,omitempty"`
+}
+
+// Port represents a network port in a single container
 type Port struct {
 	// Optional: If specified, this must be a DNS_LABEL.  Each named port
 	// in a pod must have a unique name.