mysql-test-run fix to send output to separate files if multiple masters

mysql-test/mysql-test-run.sh:
  Send output from mysqld master(s) to correct file by adding id to master.err file

mysql-test/mysql-test-run.sh

@@ -1212,8 +1212,8 @@ start_master()
            $NOT_FIRST_MASTER_EXTRA_OPTS"
   fi
 
-  CUR_MYERR=$MASTER_MYERR
-  CUR_MYSOCK=$MASTER_MYSOCK
+  CUR_MYERR=$MASTER_MYERR$1
+  CUR_MYSOCK=$MASTER_MYSOCK$1
 
   # For embedded server we collect the server flags and return
   if [ "x$USE_EMBEDDED_SERVER" = "x1" ] ; then