docker facts fail if docker is not running

[vchepkov]

If docker is installed on a node, but is not running, puppet throughs exceptions during fact collection:

Error: Facter: error while resolving custom fact "docker": 751: unexpected token at ''
Error: Facter: error while resolving custom fact "docker_server_version": undefined method `[]' for nil:NilClass

$ puppet --version
5.5.10

$ docker version
Client:
 Version:      17.05.0-ce
 API version:  1.29
 Go version:   go1.7.5
 Git commit:   89658be
 Built:        Thu May  4 22:06:25 2017
 OS/Arch:      linux/amd64
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
$ facter os
{
  architecture => "x86_64",
  family => "RedHat",
  hardware => "x86_64",
  name => "RedHat",
  release => {
    full => "7.6",
    major => "7",
    minor => "6"
  },
  selinux => {
    enabled => false
  }
}
$ puppet module list
├── puppetlabs-apt (v6.2.1)
├── puppetlabs-docker (v3.2.0)
├── puppetlabs-powershell (v2.2.0)
├── puppetlabs-reboot (v2.0.0)
├── puppetlabs-stdlib (v5.1.0)
└── puppetlabs-translate (v1.1.0)

[davejrt]

closed by pr #423