Rename os-config-applier to os-apply-config.

This is being done to reduce confusion between os-refresh-config and
os-config-applier. In order to make the transition smooth, all this
patch does is rename the element, install the now pypi available
os-apply-config, and support both the old and new directory names
for templates, allowing incremental migration of users.

Change-Id: I8c4c7679799f4e8b436ce766791f45f4c81d75f2
Merge "Rename os-config-applier to os-apply-config."