kunit: fix bug in the order of lines in debugfs logs

Fix bug in debugfs logs that causes an incorrect order of lines in the
debugfs log.

Currently, the test counts lines that show the number of tests passed,
failed, and skipped, as well as any suite diagnostic lines,
appear prior to the individual results, which is a bug.

Ensure the order of printing for the debugfs log is correct. Additionally,
add a KTAP header to so the debugfs logs can be valid KTAP.

This is an example of a log prior to these fixes:

     KTAP version 1

     # Subtest: kunit_status
     1..2
 # kunit_status: pass:2 fail:0 skip:0 total:2
 # Totals: pass:2 fail:0 skip:0 total:2
     ok 1 kunit_status_set_failure_test
     ok 2 kunit_status_mark_skipped_test
 ok 1 kunit_status

Note the two lines with stats are out of order. This is the same debugfs
log after the fixes (in combination with the third patch to remove the
extra line):

 KTAP version 1
 1..1
     KTAP version 1
     # Subtest: kunit_status
     1..2
     ok 1 kunit_status_set_failure_test
     ok 2 kunit_status_mark_skipped_test
 # kunit_status: pass:2 fail:0 skip:0 total:2
 # Totals: pass:2 fail:0 skip:0 total:2
 ok 1 kunit_status

Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>