Make update server schema 'additionalProperties' False

Nova V2.1 API has strong input validation by making validation
through JSON schema.

This patch makes update server schema 'additionalProperties' to False
as all update server extensions are implemented in V2.1.

After this, V2.1 will not allow extra arg for update server.

This patch also modify the corresponding update server tests
for extra input passed in request body-
    test_update_server_admin_password_ignored

Partially implements blueprint v2-on-v3-api

Change-Id: Ib67880d0380b539c3a5b12a14ea9ed71b7b588a3
Merge "Make update server schema 'additionalProperties' False"