sandbox: use a static path for the chroot dir

As a cgi process it creates way too many directories
if we keep the default behaviour of qssb. Another
problem at the moment is the fact that qssb does
not provide a mechanism to cleanup yet.

cgit.c

@@ -1065,6 +1065,7 @@ void enable_sandbox()
 	}
 	policy->path_policies = &dev_policy;
 	policy->namespace_options |= QSSB_UNSHARE_NETWORK;
+	policy->chroot_target_path = "/tmp/.sandbox_cgit";
 	if(qssb_enable_policy(policy) != 0)
 	{
 		fprintf(stderr, "%s", "Failed to init sandbox\n");