Parse command-line options for pumactl

[shayonj]

• Before, we would remove any non-yielding
  args, but missed to actually parse them.
  Resulting in issues like, --pidfile or
  similar args not taking any effect.

Before

pumactl start -P ~/puma.pid

...

cat ~/puma.pid
=> No such file or directory

Now

pumactl start -P ~/puma.pid

...

cat ~/puma.pid
=> 131232

---

• Remove misleading message of puma starting on pumactl exit: This way, when puma shuts down (running from pumactl), it does not end
  with "Puma is started" message. Because, the copy is dependent
  on the value of @command, the same will always point
  to start, if pumactl was issued a start, hence during
  exit, this message appeared as misleading.

Before

Puma starting in single mode...
* Version 3.10.0 (ruby 2.3.3-p222), codename: Russell's Teapot
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
^C- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2017-12-06 23:26:45 -0800 ===
- Goodbye!
Puma is started <===== Removing this message =====>

Now

Puma starting in single mode...
* Version 3.10.0 (ruby 2.3.3-p222), codename: Russell's Teapot
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop
^C- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2017-12-06 23:26:45 -0800 ===
- Goodbye!

[olleolleolle]

@nateberkopec Are you looking for a test for this bug fix?