Adds os-server-groups

This commit adds support for the os-server-groups extension. This allows
users to create scheduling policies for launching instances.
diff --git a/openstack/compute/v2/extensions/servergroups/requests.go b/openstack/compute/v2/extensions/servergroups/requests.go
new file mode 100644
index 0000000..1597b43
--- /dev/null
+++ b/openstack/compute/v2/extensions/servergroups/requests.go
@@ -0,0 +1,77 @@
+package servergroups
+
+import (
+	"errors"
+
+	"github.com/rackspace/gophercloud"
+	"github.com/rackspace/gophercloud/pagination"
+)
+
+// List returns a Pager that allows you to iterate over a collection of ServerGroups.
+func List(client *gophercloud.ServiceClient) pagination.Pager {
+	return pagination.NewPager(client, listURL(client), func(r pagination.PageResult) pagination.Page {
+		return ServerGroupsPage{pagination.SinglePageBase(r)}
+	})
+}
+
+// CreateOptsBuilder describes struct types that can be accepted by the Create call. Notably, the
+// CreateOpts struct in this package does.
+type CreateOptsBuilder interface {
+	ToServerGroupCreateMap() (map[string]interface{}, error)
+}
+
+// CreateOpts specifies a Server Group allocation request
+type CreateOpts struct {
+	// Name is the name of the server group
+	Name string
+
+	// Policies are the server group policies
+	Policies []string
+}
+
+// ToServerGroupCreateMap constructs a request body from CreateOpts.
+func (opts CreateOpts) ToServerGroupCreateMap() (map[string]interface{}, error) {
+	if opts.Name == "" {
+		return nil, errors.New("Missing field required for server group creation: Name")
+	}
+
+	if len(opts.Policies) < 1 {
+		return nil, errors.New("Missing field required for server group creation: Policies")
+	}
+
+	serverGroup := make(map[string]interface{})
+	serverGroup["name"] = opts.Name
+	serverGroup["policies"] = opts.Policies
+
+	return map[string]interface{}{"server_group": serverGroup}, nil
+}
+
+// Create requests the creation of a new Server Group
+func Create(client *gophercloud.ServiceClient, opts CreateOptsBuilder) CreateResult {
+	var res CreateResult
+
+	reqBody, err := opts.ToServerGroupCreateMap()
+	if err != nil {
+		res.Err = err
+		return res
+	}
+
+	_, res.Err = client.Post(createURL(client), reqBody, &res.Body, &gophercloud.RequestOpts{
+		OkCodes: []int{200},
+	})
+	return res
+}
+
+// Get returns data about a previously created ServerGroup.
+func Get(client *gophercloud.ServiceClient, id string) GetResult {
+	var res GetResult
+	_, res.Err = client.Get(getURL(client, id), &res.Body, nil)
+	return res
+}
+
+// Delete requests the deletion of a previously allocated ServerGroup.
+func Delete(client *gophercloud.ServiceClient, id string) DeleteResult {
+	var res DeleteResult
+	_, res.Err = client.Delete(deleteURL(client, id), nil)
+	return res
+}