7277 zdb should be able to print zfs_dbgmsg's
ztest always prints the debug messages (zfs_dbgmsg()) by calling zfs_dbgmsg_print(). We should add a flag to zdb to make it do this as well before exiting.
Reviewed by: George Wilson <firstname.lastname@example.org>
Reviewed by: Matthew Ahrens <email@example.com>
Reviewed by: Igor Kozhukhov <firstname.lastname@example.org>
Approved by: Dan McDonald <email@example.com>
Author: Pavel Zakharov <firstname.lastname@example.org>