openbsd services (openbsdservice.py): added reload(name), available(name...

...), missing(name), get_all(), get_enabled(), enabled(name), get_disabled(), disabled(name)

Add support for OpenBSD services.

Right now, declaring a service and applying state.hightstate will give the following result:
ID: sshd
Function: service.running
Result: False
Comment: The named service sshd is not available
Changes:

OpenBSD services are started via /etc/rc at boot.
This script load the system file /etc/rc.conf and the user override /etc/rc.conf.local to check wether or not a daemon should be started via the named variables 'daemon_flags'.
Non-builtin daemons are started only if the variable $pkg_scripts in /etc/rc.conf.local is set to their respective names.

This merge request provides the following functions:
  - reload(): simply reloads the service via /etc/rc.d/daemon -f reload,
  - available(): tests if a daemon is present in /etc/rc.d,
  - missing(): tests if a daemon is absent of /etc/rc.d,
  - get_all(): returns all the available services in /etc/rc.d,
  - get_enabled(): returns the available daemons enabled in /etc/rc.conf or /etc/rc.conf.local,
  - enabled(): tests if a daemon is enabled,
  - get_disabled(): returns the available daemons disabled in /etc/rc.conf or /etc/rc.conf.local,
  - disabled():  tests if a daemon is disabled.

With this patch, the state.highstate output is:
ID: sshd
Function: service.running
Result: True
Comment: The service sshd is already running
Changes:

However, the patch doesn't provide the ability to set the status of a deamon, since it requires to write in /etc/rc.conf.local file, which is possible via:
salt-master.rc.conf:
  file:
    - append
    - name: /etc/rc.conf.local
    - source: salt://openbsd-salt/daemons/salt/master/rc.conf.local
[...]

And salt://openbsd-salt/daemons/salt/master/rc.conf.local contents:
pkg_scripts="$pkg_scripts salt_master"
salt_master_flags="-d"
salt_master_user="" # root