Tests: use shared session cache in ssl_verify_client for coverage.

This enables tests for session removal from shared cache on client verify error.
diff --git a/ssl_verify_client.t b/ssl_verify_client.t
index 002ec5a..ef86c7f 100644
--- a/ssl_verify_client.t
+++ b/ssl_verify_client.t
@@ -56,6 +56,9 @@
 
     add_header X-Verify x$ssl_client_verify:${ssl_client_cert}x;
 
+    ssl_session_cache shared:SSL:1m;
+    ssl_session_tickets off;
+
     server {
         listen       127.0.0.1:8080;
         server_name  localhost;