We want to eventually disable NFS by default. Let's add a big warning when that's not set so tools relying on NFS access can set mount: all explicitely before the default is changed.
Also cleans up the manifest handling a bit. Build service specific options (image and mount) are no longer written to the manifest if the buildservice ws type is not enabled.
Bug: T346605 Change-Id: Ie435ce90f93e01f2ff925726275f92b5af2c7dc3