When running the test in valgrind mode, pass the right flags to show memory...

When running the test in valgrind mode, pass the right flags to show memory leaks stack traces but only including the "definitely lost" items.

tests/support/server.tcl

@@ -176,7 +176,7 @@ proc start_server {options {code undefined}} {
     set stderr [format "%s/%s" [dict get $config "dir"] "stderr"]
 
     if {$::valgrind} {
-        exec valgrind --suppressions=src/valgrind.sup src/redis-server $config_file > $stdout 2> $stderr &
+        exec valgrind --suppressions=src/valgrind.sup --show-reachable=no --show-possibly-lost=no --leak-check=full src/redis-server $config_file > $stdout 2> $stderr &
     } else {
         exec src/redis-server $config_file > $stdout 2> $stderr &
     }