MDEV-22150: Symlink and move test client plugins to client plugin path

Without this, the mtr will fail to load client plugins and the following
tests would fail:

- main.plugin_auth_qa_2
- main.plugin_auth_qa_3
- main.plugin_auth
- plugins.multiauth
- plugins.auth_ed25519

debian/mariadb-test.install

@@ -2,6 +2,9 @@ usr/bin/mariadb-client-test
 usr/bin/mariadb-client-test-embedded
 usr/bin/mariadb-test
 usr/bin/mariadb-test-embedded
+usr/lib/*/libmariadb3/plugin/auth_test_plugin.so
+usr/lib/*/libmariadb3/plugin/qa_auth_client.so
+usr/lib/*/libmariadb3/plugin/qa_auth_interface.so
 usr/lib/mysql/plugin/adt_null.so
 usr/lib/mysql/plugin/auth_0x0100.so
 usr/lib/mysql/plugin/auth_test_plugin.so
@@ -13,7 +16,6 @@ usr/lib/mysql/plugin/ha_example.so
 usr/lib/mysql/plugin/ha_test_sql_discovery.so
 usr/lib/mysql/plugin/libdaemon_example.so
 usr/lib/mysql/plugin/mypluglib.so
-usr/lib/mysql/plugin/qa_auth_client.so
 usr/lib/mysql/plugin/qa_auth_interface.so
 usr/lib/mysql/plugin/qa_auth_server.so
 usr/lib/mysql/plugin/test_versioning.so

debian/rules

@@ -146,6 +146,13 @@ endif
 	# Install libmariadbclient.a compatibility link
 	ln -s libmariadb.a $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadbclient.a
 
+	# Symlink plugins that are used by both server and client and thus need to
+	# load from the libmariadb path as well
+	ln -s ../../../mysql/plugin/auth_test_plugin.so $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadb3/plugin/auth_test_plugin.so
+	ln -s ../../../mysql/plugin/qa_auth_interface.so $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadb3/plugin/qa_auth_interface.so
+	# Move test plugins that are only needed by the client to the libmariadb path
+	mv -v $(TMP)/usr/lib/mysql/plugin/qa_auth_client.so $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadb3/plugin/
+
 override_dh_fixperms:
 	dh_fixperms
 	chmod 04755 debian/mariadb-server-10.5/usr/lib/mysql/plugin/auth_pam_tool_dir/auth_pam_tool