MDEV-4748 - metadata_lock_info plugin

- include metadata_lock_info plugin into debian packages
- ignore metadata_lock_info plugin in mysqld--help test
- let test suite run with built-in metadata_lock_info plugin

debian/dist/Debian/mariadb-server-10.0.files.in

@@ -4,6 +4,7 @@ usr/lib/mysql/plugin/ha_sequence.so
 usr/lib/mysql/plugin/ha_sphinx.so
 usr/lib/mysql/plugin/handlersocket.so
 usr/lib/mysql/plugin/locales.so
+usr/lib/mysql/plugin/metadata_lock_info.so
 usr/lib/mysql/plugin/query_cache_info.so
 usr/lib/mysql/plugin/query_response_time.so
 usr/lib/mysql/plugin/semisync_master.so

debian/dist/Ubuntu/mariadb-server-10.0.files.in

@@ -4,6 +4,7 @@ usr/lib/mysql/plugin/ha_sequence.so
 usr/lib/mysql/plugin/ha_sphinx.so
 usr/lib/mysql/plugin/handlersocket.so
 usr/lib/mysql/plugin/locales.so
+usr/lib/mysql/plugin/metadata_lock_info.so
 usr/lib/mysql/plugin/query_cache_info.so
 usr/lib/mysql/plugin/query_response_time.so
 usr/lib/mysql/plugin/semisync_master.so

mysql-test/t/mysqld--help.test

@@ -28,7 +28,7 @@ perl;
               thread-concurrency super-large-pages mutex-deadlock-detector
               connect null-audit aria oqgraph sphinx thread-handling
               test-sql-discovery rpl-semi-sync query-cache-info
-              query-response-time locales/;
+              query-response-time metadata-lock-info locales/;
 
   # And substitute the content some environment variables with their
   # names:

plugin/metadata_lock_info/mysql-test/metadata_lock_info/suite.pm

@@ -2,7 +2,8 @@ package My::Suite::Metadata_lock_info;
 
 @ISA = qw(My::Suite);
 
-return "No Metadata_lock_info plugin" unless $ENV{METADATA_LOCK_INFO_SO};
+return "No Metadata_lock_info plugin" unless $ENV{METADATA_LOCK_INFO_SO} or
+  $::mysqld_variables{'metadata-lock-info'} eq "ON";;
 
 bless { };