Added new test to check that "CONFIG appendonly no" actually kills the...

Added new test to check that "CONFIG appendonly no" actually kills the background AOF operation in progress if any.

tests/unit/aofrw.tcl

 start_server {tags {"aofrw"}} {
+
+    test {Turning off AOF kills the background writing child if any} {
+        r config set appendonly yes
+        waitForBgrewriteaof r
+        r multi
+        r bgrewriteaof
+        r config set appendonly no
+        r exec
+        set result [exec cat [srv 0 stdout] | tail -n1]
+    } {*Killing*AOF*child*}
+
     foreach d {string int} {
         foreach e {ziplist linkedlist} {
             test "AOF rewrite of list with $e encoding, $d data" {