MDEV-8664 - plugins.show_all_plugins --embedded fails in buildbot

Failed attempt to load dynamic library with STB_GNU_UNIQUE symbol may corrupt
internal dynamic linker data sructures. This looks like libdl bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=14577

In embedded mode "show plugins soname" fails to dlopen ha_mroonga.so (which
has STB_GNU_UNIQUE) due to undefined reference to wsrep_forced_binlog_format.
It crashes later in subsequent call to dlopen() from  pthread_exit().

Disabled plugins.show_all_plugins until dlopen() bug is fixed.

mysql-test/suite/plugins/t/show_all_plugins.test

@@ -3,6 +3,7 @@ if (!$HA_EXAMPLE_SO) { skip requires ha_examples.so; }
 if (!$LIBDAEMON_EXAMPLE_SO) { skip requires libdaemon_examples.so; }
 if (!$UDF_EXAMPLE_SO) { skip requires udf_example.so; }
 if (!$EXAMPLE_KEY_MANAGEMENT_SO) { skip requires example_key_management.so; }
+if (`SELECT VERSION() LIKE '%embedded%'`) { skip Disabled for embedded until MDEV-8664 is resolved; }
 
 flush status;
 show status like '%libraries%';