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 +1,51 @@
+#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
+The `volumetype` parameter is configurable based on what types are available in
+your zone.  Check the [diskTypes](https://cloud.google.com/compute/docs/reference/latest/diskTypes/list)
+active API call for more details.
+
+## Limitations
+This driver does not currently support snapshot functionality.

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)