Do not effectively set DEBUG_DBUG='d' by setting DEBUG_DBUG='-d,...'.
Instead, restore the saved value of DEBUG_DBUG.

Also, split the test innodb_fts.innodb_fts_misc_debug into
innodb_fts.crash_recovery and innodb_fts.misc_debug, and enable
these tests for --valgrind, the latter test for --embedded,
and the former tests for the non-debug server.