BUG#25659 - memory leak via "plugins" test

- Added suppressions for dlopen to make plugin test pass.
- Do not pass empty string to mysqld, since my_getopt is
  not capable to handle it.
- Re-enabled trailing UNINSTALL PLUGIN statement of plugin.test.

The memory leak described in the bug report happens in libdl, not
in mysqld. On some valgrind installations this error is suppressed
by default, no idea why it isn't suppressed on pb-valgrind.

<observation>
If library remains open after thread has finished, and is closed by
another thread, we get memory leak. But in case library is opened and
closed by the same thread no leak occurs.
</observation>

1 files changed, 5 insertions, 1 deletions

diff --git a/mysql-test/lib/mtr_io.pl b/mysql-test/lib/mtr_io.pl
index 570a58875c2..aa671c0f4f7 100644
--- a/mysql-test/lib/mtr_io.pl
+++ b/mysql-test/lib/mtr_io.pl
@@ -120,7 +120,11 @@ sub mtr_get_opts_from_file ($) {
       $arg =~ s/\$(\w+)/envsubst($1)/ge;
 
 #      print STDERR "ARG: $arg\n";
-      push(@args, $arg);
+      # Do not pass empty string since my_getopt is not capable to handle it.
+      if (length($arg))
+      {
+        push(@args, $arg)
+      }
     }
   }
   close FILE;