Moved install.inf related code from save_network to new client.

save_network client used to be run in the end of first stage. However,
installer needs configured network at the beginning of first stage since
first and second stages were merged. Install.inf is one of resources
usable for "automatic" network configuration.
Refactoring: "new" InstInstallInfClient
Refactoring: InstInstallInfClient - splitting methods
Dropped dead code
Refactoring: removed globals from InstInstallInfClient