Fix mysql_plugin test to handle version XXa

mysql-test/t/mysql_plugin.test

@@ -372,11 +372,11 @@ let $MYSQL_PLUGIN_CMD= $MYSQL_PLUGIN -n --datadir=$MYSQL_DATADIR --basedir=$MYSQ
 --echo # Show the help.
 --echo #
 replace_result $MYSQL_PLUGIN mysql_plugin;
---replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/
+--replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/ /XX[a-z]/XX/
 --exec $MYSQL_PLUGIN --help
 
 replace_result $MYSQL_PLUGIN mysql_plugin;
---replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/
+--replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/ /XX[a-z]/XX/
 --exec $MYSQL_PLUGIN --version
 
 #