Adds entries for missing parameters in PLUMgrid plugin

Three configuration parameters were missing for the PLUMgrid plugin.
In this patch all those three have been properly added.

Change-Id: If070aa5eb35678d0984470ebcd43fd99e08bcc8a
Closes-Bug: #1255808
(cherry picked from commit 500a32f4f8e8526ba075b61f336cf91dc9d8c652)
Merge "Adds entries for missing parameters in PLUMgrid plugin" into stable/havana