Configuration: Fix deps issues with service between 2 top services.
tests: Add a simple SKIPPED test for Service.
service: Rewrite _process_dependencies() and prepare()

Clean _process_dependencies() code in ServiceGroup which
abled to refactor this code in prepare().
_process_dependencies() was removed and replace by a simpler
_launch_action().
milkcheck.conf: add "reverse_actions" example
BaseEntity: Fix bad inherits_from conditions

* If target nodeset is empty, target should not be inherited
* If desc is '', desc should not be inherited
Changelog for 'Fix bad inherits_from conditions'
Engine: Remove compat code for $(...)
Engine: Subservices should have a parent when added with add_inter_dep()
tests: Add test for ConfigParser data checking
error: Better error message when requiring a missing dep
Config: Better error handling when facing unknown rule in config file.
Engine: Code cleaning in ActionManager.perform_action().

Remove useless tests and assert, to simplify code.
Engine: Action manages SKIPPED and not Service.

- ServiceGroup has a correct status when fully SKIPPED or MISSING.
- Move skipped() method and rename it to to_skip()
- Add a test checking that a service with empty target and DEP_ERROR
is not skipped if its action has real target and could be run.
Engine: Remove fake actions in ServiceGroup
Cli: Add --nodeps option

This option disables all dependencies for the required services.
Release 0.11.1