REGTESTS: fix the race conditions in log_uri.vtc

A "Connection: close" header is added to responses to avoid any connection
reuse. This should avoid any "HTTP header incomplete" errors.
diff --git a/reg-tests/log/log_uri.vtc b/reg-tests/log/log_uri.vtc
index 6993b7c..6dd50d2 100644
--- a/reg-tests/log/log_uri.vtc
+++ b/reg-tests/log/log_uri.vtc
@@ -5,7 +5,7 @@
 
 server s1 {
     rxreq
-    txresp
+    txresp  -hdr "Connection: close"
 } -repeat 4 -start
 
 syslog Slg_1 -level info {