Fix naming of output files in tests, which were out of order and
sometimes incorrectly named.

Remove check for w->path being NULL, as it is always required to
be non-NULL.

In t2204-job-info.t and t2205-job-info-security.t, fixup helper
functions in tests for correctness and clarity.

Includes:

- For portability, use "sleep 300" instead of "sleep inf"
- Rename test jobspecs from "test" and "test-all", to "sleeplong" and
  "sleeplong-all-rsrc".
- In helper functions, declare local variables local
- In helper functions, check for failures by chaining commands

When watching the main job eventlog, when reaching the end of
the eventlog (i.e. "clean" event), return ENODATA to the user.

Update job-info watch tests for behavior change to watch, in which
ENODATA is immediately returned upon reaching the end of the main
job eventlog.  Add new tests for coverage as well.

As a consequence of the main eventlog returning ENODATA at the
of the eventlog, a hang can no longer occur while waiting for
a guest namespace to be created.

Update comments to note this fact.

Closes flux-framework#2361

Add test for monitoring a guest namespace eventlog, but the guest
namespace will never be created.

After it has been determined that a guest eventlog has been migrated
to the primary KVS namespace, there is no need to "watch" the eventlog
in the namespace.  We know that the eventlog is complete, so instead
"lookup" the eventlog and send the eventlog to the caller.

When watching a guest eventlog in the guest namespace, return ENODATA
when the guest eventlog has reached its end.  We know the guest
eventlog has reached the end when the guest namespace has been removed
and ENOTSUP is received.

Closes flux-framework#2338

Adjust comments on tests, as wait-event no longer "hangs" when an
event doesn't happen, but rather it "times out" if the event doesn't
occur in the time period expected.

In the kvs-watch module, there is a small possibility the namespace
remove event could be received before the last bits of data from
a watch are sent to a watcher.

- user write to eventlog, kvs commits write, sends setroot event
- user deletes namespace, kvs sends namespace-remove event
- kvs-watch receives setroot event, does lookupat on key
- kvs-watch receives namespace-remove event BEFORE lookupat returns,
  sends ENOTSUP to watchers
- response from lookupat arrives after ENOTSUP sent

To workaround this, in the job-info module, always track how much data
from the guest eventlog has been sent.  When the namespace has been
removed, fallthrough from the guest namespace to the primary KVS
namespace, and check that all data that could be sent to the caller
has been sent.

Fixes flux-framework#2386

With the primary job eventlog and guest eventlogs now automatically
sending ENODATA upon completion, attach no longer needs to call
flux_job_event_watch_cancel() under several circumstances.

In particular:

- it does not need to call flux_job_event_watch_cancel()
  after receiving the "clean" event in the primary job eventlog.
- it does not need to monitor EOF counts in guest.output, the
  output will complete when it reaches the end.