Add description to policies in server_password.py
Add description to policies in server_password.py

The 'discoverable' policy is not documented as it will be removed in a
future change.

blueprint policy-docs

Change-Id: I57e794a20fb882b72f251033ad612397a1a5058f

rajalokan/nova,klmitch/nova,jianghuaw/nova,mahak/nova,Juniper/nova,rajalokan/nova,Juniper/nova,jianghuaw/nova,openstack/nova,klmitch/nova,mikalstill/nova,gooddata/openstack-nova,mikalstill/nova,phenoxim/nova,vmturbo/nova,jianghuaw/nova,vmturbo/nova,rahulunair/nova,mahak/nova,phenoxim/nova,openstack/nova,mikalstill/nova,gooddata/openstack-nova,vmturbo/nova,rahulunair/nova,jianghuaw/nova,rahulunair/nova,gooddata/openstack-nova,openstack/nova,mahak/nova,klmitch/nova,rajalokan/nova,Juniper/nova,gooddata/openstack-nova,klmitch/nova,rajalokan/nova,Juniper/nova,vmturbo/nova