client.c: Created print_update_link() to get and print the update link

print_update_link() calls the server to get the link needed by the collect
agent to update, printing the link to the standard output.

Signed-off-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Acked-by: Diego Giovane Pasqualin <dgp06@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>