Adds id in update_floatingip API in PLUMgrid plugin driver

The id parameter is missing in the update_floatingip API, this patch
adds it.

Change-Id: I7407fe34628f8ef03a946a11fea9dad8b0f6c256
Closes-Bug: #1257119
(cherry picked from commit b6e23caddf05457b2337ac03d33b066a36aad154)