Migrate rackspace/gophercloud -> gophercloud/gophercloud

Update vendor libraries

vendor/github.com/gophercloud/gophercloud/MIGRATING.md

@@ -0,0 +1,32 @@
+# Compute
+
+## Floating IPs
+
+* `github.com/gophercloud/gophercloud/openstack/compute/v2/extensions/floatingip` is now `github.com/gophercloud/gophercloud/openstack/compute/v2/extensions/floatingips`
+* `floatingips.Associate` and `floatingips.Disassociate` have been removed.
+* `floatingips.DisassociateOpts` is now required to disassociate a Floating IP.
+
+## Security Groups
+
+* `secgroups.AddServerToGroup` is now `secgroups.AddServer`.
+* `secgroups.RemoveServerFromGroup` is now `secgroups.RemoveServer`.
+
+## Servers
+
+* `servers.Reboot` now requires a `servers.RebootOpts` struct:
+
+  ```golang
+  rebootOpts := &servers.RebootOpts{
+          Type: servers.SoftReboot,
+  }
+  res := servers.Reboot(client, server.ID, rebootOpts)
+  ```
+
+# Identity
+
+## V3
+
+### Tokens
+
+* `Token.ExpiresAt` is now of type `gophercloud.JSONRFC3339Milli` instead of
+  `time.Time`