Deprecate pluginsync setting

The pluginsync setting should be deprecated and a warning issued if the setting is specified explicitly on the command line or puppet.conf. In 5.x, the setting will be removed. The motivation is because catalog and plugins can be inconsistent with the following combinations:

pluginsync=false

use_cached_catalog=false

Will cause the agent to get the latest catalog, but use older plugins. The new catalog may reference property/parameters that the old plugins don't know how to manage, or the agent may not have any plugins. Worse, the agent run may succeed, but due to semantic differences between the catalog and plugins, not achieve the desired state.

OR

pluginsync=true

use_cached_catalog=true

Will cause the agent to use an old catalog with the latest plugins. The new pluginsync may have removed support for managing property/parameters contained in the catalog.