[python-neutronclient]:Fix for neutron policy-list
[python-neutronclient]:Fix for neutron policy-list

Modifying 'policies' in EXTED_PLURALS dict to 'policys' so that the
right functin i.e list_policys() gets called bu neutron.

Closes-Bug: #1700581

Juniper/python-neutronclient,Juniper/python-neutronclient