6295 metaslab_condense's dbgmsg should include vdev id

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Andriy Gapon <avg@freebsd.org>
Reviewed by: Xin Li <delphij@freebsd.org>
Reviewed by: Justin Gibbs <gibbs@scsiguy.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Author: Joe Stein <joe.stein@delphix.com>

illumos/illumos-gate@daec38ecb4fb5e73e4ca9e99be84f6b8c50c02fa