client.c: Added parameter to getUpdateLink() and getAgentVersion() calls

The parameter "OS" specifies the operating system where the client is
being run.

Signed-off-by: Adriano da Luz <al08@c3sl.ufpr.br>
Acked-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>