engine_page: add compatiblePort() to src

compatiblePort() is defined vdsm/vdsm_reg/engine.py.in
(previous version of engine_page.py) delivered in
%{python_sitelib}/ovirt_config_setup/engine.py.
Instead of to keep this old file in vdsm tree just for
one function we should move the function to the new
project ovirt-node-plugin-vdsm and remove such file.

Change-Id: I8eec07e576dce8b3ce8c064897a2e47c674891f6
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>