run-postinsts: add more logging to the log file to make things clearer

run-postinsts: add more logging to the log file to make things clearer

When all postinsts scripts succeed at system startup, it's very possible
that the log file /var/log/postinstall.log is empty. This is kind of
confusing, as that file is supposed to hold information about the postinsts.

Add more logging to the log file to make things clearer.

(From OE-Core rev: d60926b3fc4ba5780aef5b5226d05170892a7133)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>