Only setup cmdline_myslslap if exe_mysqlslap defined

mysql-test/mysql-test-run.pl

@@ -1544,6 +1544,8 @@ sub environment_setup () {
   # ----------------------------------------------------
   # Setup env so childs can execute mysqlslap
   # ----------------------------------------------------
+  if ( $exe_mysqlslap )
+  {
     my $cmdline_mysqlslap=
       "$exe_mysqlslap -uroot " .
       "--port=$master->[0]->{'port'} " .
@@ -1556,6 +1558,7 @@ sub environment_setup () {
 	" --debug=d:t:A,$path_vardir_trace/log/mysqlslap.trace";
     }
     $ENV{'MYSQL_SLAP'}= $cmdline_mysqlslap;
+  }
 
   # ----------------------------------------------------
   # Setup env so childs can execute mysqlimport