fix typo in docker_version definition, handle origin pre-existing symlink

[maxamillion]

@sdodson please review

[sdodson]

👍

Fixes this error when /etc/origin exists already:

Running transaction
ln: failed to create symbolic link ‘/etc/origin/openshift’: File exists
error: %pre(openshift-1.0.5-3.git.5410.489ec06.el7.centos.x86_64) scriptlet failed, exit status 1
Error in PREIN scriptlet in rpm package openshift-1.0.5-3.git.5410.489ec06.el7.centos.x86_64

@brenton merge if it looks good to you.

[maxamillion]

looking at TravisCI, the failure appears to be unrelated ... so that's fun :)

[brenton]

[merge]

[openshift-bot]

continuous-integration/openshift-jenkins/merge SUCCESS (https://ci.openshift.redhat.com/jenkins/job/merge_pull_requests_origin/3142/) (Image: devenv-fedora_2240)

[openshift-bot]

Evaluated for origin merge up to 820c7a8