Bugfixes and updates for GCE driver

This updates a few things relating to bugs found during
initial testing and includes some features to minimize
the configuration of the driver.

.docs/user-guide/gce.md

@@ -0,0 +1,52 @@
+#Google Compute Engine
+
+The Google Cloud
+
+---
+
+## Overview
+The GCE registers a storage driver named `gce` with the `REX-Ray`
+driver manager and is used to connect and manage Google Compute Engine storage.
+
+## Pre-Requisites
+In order to leverage the GCE driver, REX-Ray must be located on the
+running GCE instane that you wish to receive storage.  There must also
+be a `json key` file for the credentials that can be retrieved from the [API
+portal](https://console.developers.google.com/apis/credentials).
+
+## Configuration
+The following is an example configuration of the GCE driver.
+
+```yaml
+gce:
+  keyfile: path_to_json_key
+```
+
+For information on the equivalent environment variable and CLI flag names
+please see the section on how non top-level configuration properties are
+[transformed](./config/#all-other-properties).
+
+## Activating the Driver
+To activate the XtremIO driver please follow the instructions for
+[activating storage drivers](/user-guide/config#activating-storage-drivers),
+using `gce` as the driver name.
+
+## Examples
+Below is a full `rexray.yml` file that works with GCE.
+
+```yaml
+rexray:
+  storageDrivers:
+  - gce
+gce:
+  keyfile: /certdir/cert.json
+```
+
+## Configurable items
+
+https://cloud.google.com/compute/docs/reference/latest/diskTypes/list
+
+## Limitations
+- This driver does not currently support snapshot functionality.
+- Debian 8.2 forced mounts via pre-emption results in Input/Output error until
+remounted 

README.md

@@ -12,6 +12,7 @@ Irrespective of platform, `REX-Ray` provides common functionality for the follow
 - OpenStack (Cinder)
 - EMC ScaleIO
 - EMC XtremIO
+- Google Compute Engine (GCE)
 - ..more coming
 
 ## Operating System Support
@@ -36,8 +37,8 @@ The following command will install the REX-Ray client-server tool.  If using `Ce
 
 ```bash
 $ export REXRAY_STORAGEDRIVERS=ec2
-$ export AWS_ACCESS_KEY=access_key
-$ export AWS_SECRET_KEY=secret_key
+$ export AWS_ACCESSKEY=access_key
+$ export AWS_SECRETKEY=secret_key
 $ rexray volume get
 
 - providername: ec2
@@ -53,8 +54,8 @@ Additionally, it can be ran as a service to support `Docker`, `Mesos`, and other
 
 ```bash
 $ export REXRAY_STORAGEDRIVERS=ec2
-$ export AWS_ACCESS_KEY=access_key
-$ export AWS_SECRET_KEY=secret_key
+$ export AWS_ACCESSKEY=access_key
+$ export AWS_SECRETKEY=secret_key
 $ rexray service start
 Starting REX-Ray...SUCESS!
 

core/drivers_storage.go

@@ -248,7 +248,7 @@ func (r *sdm) GetVolumeMapping() ([]*BlockDevice, error) {
 	for _, driver := range r.drivers {
 		blockDevices, err := driver.GetVolumeMapping()
 		if err != nil {
-			return []*BlockDevice{}, errors.ErrDriverBlockDeviceDiscovery
+			return []*BlockDevice{}, err
 		}
 
 		if len(blockDevices) > 0 {

drivers/os/linux/linux.go

@@ -120,7 +120,7 @@ func (d *driver) Format(
 	if overwriteFs || !fsDetected {
 		switch newFsType {
 		case "ext4":
-			if err := exec.Command("mkfs.ext4", deviceName).Run(); err != nil {
+			if err := exec.Command("mkfs.ext4", "-F", deviceName).Run(); err != nil {
 				return fmt.Errorf(
 					"Problem creating filesystem on %s with error %s",
 					deviceName, err)