salt.modules.timezone: It is not enough to check for timedatectl existence

Description of Issue/Question

salt.modules.timezone only checks if timedatectl exists but this not enough: dbus-daemon must be installed and running as well. Otherwise you will get an error like

minion32.example.org:
----------
          ID: Europe/Berlin
    Function: timezone.system
      Result: False
     Comment: Unable to compare desired timezone 'Europe/Berlin' to system timezone: timedatectl failed: Failed to create bus connection: No such file or directory
     Started: 13:58:54.247773
    Duration: 7.331 ms
     Changes:
----------

Steps to Reproduce Issue

1. Install Debian Jessie (8.7 as of today) in minbase variant using debootstrap (debootstrap --variant=minbase --arch amd64 jessie /mnt/debian http://httpredir.debian.org/debian).

2. Create a timezone.sls state with the following content:

Europe/Berlin:
  timezone.system

3. Execute the state on your fresh system set up in step 1.

Versions Report

# salt --versions-report
Salt Version:
           Salt: 2016.11.2

Dependency Versions:
           cffi: 0.8.6
       cherrypy: Not Installed
       dateutil: 2.2
          gitdb: 0.5.4
      gitpython: 0.3.2 RC1
          ioflo: Not Installed
         Jinja2: 2.9.4
        libgit2: Not Installed
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.4.2
   mysql-python: 1.2.3
      pycparser: 2.10
       pycrypto: 2.6.1
         pygit2: Not Installed
         Python: 2.7.9 (default, Jun 29 2016, 13:08:31)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 14.4.0
           RAET: Not Installed
          smmap: 0.8.2
        timelib: Not Installed
        Tornado: 4.2.1
            ZMQ: 4.0.5

System Versions:
           dist: debian 8.7
        machine: x86_64
        release: 3.16.0-4-amd64
         system: Linux
        version: debian 8.7

(Salt from https://repo.saltstack.com/#debian)

Start with salt.modules.timezone and the timezone.system state described in the report. Reproduce the minbase Debian Jessie setup and inspect how timedatectl availability is checked before the state runs. Done means the missing dbus-daemon condition is handled without the reported timedatectl bus-connection failure, with coverage for the reproduction.