Fix onion service version validation in securedrop-admin install
Fix onion service version validation in securedrop-admin install

This was fallout from introducing non-interactive configuration
validation during the install operation.

The SiteConfig._config_in_progress attribute was only being populated
in user_prompt_config, so the v3 validator would never see v2 enabled
during the install validation step, causing a spurious validation
complaint if only v2 were enabled. This change copies the loaded
config to _config_in_progress before calling clean_config, so
validators can check the values of other configuration values.

conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop