This is an attempt to diagnose why it's flaky in the releng testbeds
but not when I run it. This change will be backed out once we get
new testbed output.
If set, then when rump daemonizes, it opens the path in RUMP_STDOUT
and redirects fd 1 to that (which mostly gets the kernel console
output), and opens the path in RUMP_STDERR and redirects fd 2 to that
(no idea what this gets but it's probably good to record if it ever
gets anything).
This will allow tests that rely on rump_server daemons to stash the
output for diagnostics in case, e.g., the rump kernel crashes.
PR bin/58112
Also, add rump_daemonize_begin() / rump_daemonize_end() to help
with the "can't daemon() after pthread_create()" problem. Applications
could accomplish the same, but since it's such a common operation,
provide a little help.
riastradh