Ensure git safe directory is templated properly

We're missing `=` in gitconfig template. That template is being used
only when `git` is missing from the image template, which is the reason
why it slipped attention.

Change-Id: I602cb8b603306241e601cffc2324cb618a1dc792

templates/gitconfig.j2

@@ -4,6 +4,6 @@
 {% if openstack_hosts_git_safe_directories is defined %}
 [safe]
 {% for dir in openstack_hosts_git_safe_directories %}
-       directory {{ dir }}
+       directory = {{ dir }}
 {% endfor %}
 {% endif %}