Do not override cloud-init cloud_config_modules

In the past it may have been necessary to do this but it causes problems
for users of advanced features. We should be able to operate with the
default OS configuration of cloud-init.

Change-Id: Ic26bffb17b1870d656fea72cf3da3dfe2b7f44d0
Closes-Bug: #1263297
Merge "Do not override cloud-init cloud_config_modules"