This commit replaces the hand-crafted config processing by the use of
the 'List_model' utility. This has the following advantages:
- The parsing follows a common formalism that makes the code
easier to maintain and to understand. Several parts of the code
had to be changed (for the better) to make it fit the list model
approach. E.g., the child states have become more expressive
and logical.
- In the common case, the XML data is traversed only once, which
increases the parsing speed in dynamic scenarios.
- The code becomes easier to optimize. In particular, the patch skips
the re-evaluation of the session routing if no service is affected
by the config change.
The patch also revisits the init test by removing overly long sleep
phases and extending a few sleep phases that were too short when
executing the test on Qemu.
Issue #4068
