We had
   /etc/init.d/wrs-boot-procedure: line 104: tee: not found

because tee is not in /bin; we need to always use "busybox tee".
This adds a variable TEE="busybox tee" to make it easier to remind, at
later edits, and fit in 80 columns at the same time.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>