Get rid of write_safe

Current glibc implementation is safe. Kernel does this atomically,
and write is actually implemented through writev. So if write is
async-signal-safe, than writev pretty much must be too.
Base mkostemp_safe on mkostemp

It is nice to wrap umask handling and return convention,
but glibc's mkostemp is async-signal-safe already.
manager: print ephemeral information about running jobs' timeouts (v2)

This reverts commit 28c758de94bc8ba97b89d9dab3f517cf466978d0
but makes job_coldplug smarter.

In (v1) I changed the job start timestamp to be always set, so the
start time can be reported in the cylon eye message.  The bug was that
when deserializing jobs, they would be ignored if their start
timestamp was unset which was synonymous with no timeout. But after
the change, jobs would have a start timestamp set despite having no
timeout. After deserialization they would be considered immediately
expired. Fix this by checking if the timeout is not zero when
considering jobs for expiration.
manager: requeue the cylon eye for 5s later when a job finishes

We'd reqeue the next status update very soon after. Change it so that we wait
for full 5s without any job status changes until we print anything.