test-util-sockets: Clean up SocketAddress construction

test-util-sockets: Clean up SocketAddress construction

The thread functions build the SocketAddress from global variable
@abstract_sock_name and the tight flag passed as pointer
argument (either NULL or (gpointer)1).  There is no need for such
hackery; simply pass the SocketAddress instead.

While there, dumb down g_rand_int_range() to g_random_int().

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>