Fix environment variable

An updated in OpenShift configuration changed the $HOME environment variable from $HOME to $OPENSHIFT_HOMEDIR

The fix permits to solve the following error when deploying

~~~
remote: /var/lib/openshift/477155af8f6b4938b1ebff4e6e801e9f/app-root/runtime/repo/.openshift/action_hooks/build: line 18: cd: /git/jbosswiki.git: No such file or directory
remote: /var/lib/openshift/477155af8f6b4938b1ebff4e6e801e9f/app-root/runtime/repo/.openshift/action_hooks/build: line 20: config: Permission denied
remote: /var/lib/openshift/477155af8f6b4938b1ebff4e6e801e9f/app-root/runtime/repo/.openshift/action_hooks/build: line 21: config: Permission denied
remote: /var/lib/openshift/477155af8f6b4938b1ebff4e6e801e9f/app-root/runtime/repo/.openshift/action_hooks/build: line 22: config: Permission denied
remote: An error occurred executing 'gear postreceive'
~~~