tests: fix races in and standardize the tail tests

tests: fix races in and standardize the tail tests

* tests/tail-2/F-vs-missing.sh: Use standard "fastpoll" options
(-s.1 --max-unchanged-stats=1) to speedup the non-inotify case.
Add the non-inotify case to the test. `wait` on the background
tail process to terminate which should avoid the need for the
non standard `retry_delay_ cleanup ...` on NFS.
* tests/tail-2/F-vs-rename.sh: Remove 'out' at the start of the loop,
to avoid a race in checking its contents.  Also ensure 'a' & 'b'
files are present before the tail process starts.  Use the standard
"fastpoll" options as above.
* tests/tail-2/f-vs-rename.sh: Likewise.
* tests/tail-2/append-only.sh: Use more standard variable names.
* tests/tail-2/flush-initial.sh: Use "fastpoll" options for
non-inotify platforms.  Also `wait` on the background tail to avoid
stray processes and file cleanup issues on NFS.
* tests/tail-2/inotify-hash-abuse.sh: Always run non-inotify case.
Use "fastpoll" options.  Use a more standard retry_delay_ instead
of a hardcoded sleep loop.  Add a `wait` on the background tail.
* tests/tail-2/inotify-hash-abuse2.sh: Likewise.
* tests/tail-2/inotify-rotate-resources.sh: Wait just on the
specific tail $pid needed.
* tests/tail-2/inotify-rotate.sh: Use "fastpoll" options.
* tests/tail-2/pid.sh: Use standard variable names.
Add a `wait` on the background tails.
* tests/tail-2/pipe-f2.sh: Likewise.
* tests/tail-2/tail-n0f.sh: Likewise.
* tests/tail-2/retry.sh: Use "fastpoll" options.
* tests/tail-2/symlink.sh: Likewise.
* tests/tail-2/wait.sh: Likewise.  Speedup by using sub second
parameters to timeout(1).  Improve the part ensuring that
-F never follows a renamed file.
* tests/tail-2/infloop-1.sh: Remove invalid test.  tail(1) was not
being passed the --pid=$yes_pid option, retry_delay_ wasn't used
to avoid races, and yes could write huge files before being killed.
* tests/local.mk: Remove the invalid test reference.
* tests/tail-2/assert-2.sh: Rewrite using retry_delay_().  Since
no longer hardcoding large delays, remove the VERY_EXPENSIVE tag.
* tests/tail-2/assert.sh: Likewise.