tee: add some basic tests

The cases are ordered in such a way that we naturally progress through
the functionality, with the earliest failures perhaps shedding light on
any later failures.

sysutils/porch is used for one test if it's available, just to cleanly
check that SIGINT is being ignored properly.

Reviewed by: des, emaste

(cherry picked from commit 85ff0b08ee699ff323404727998993275b4d2e2a)