feature #21502 Persist app bootstrapping logs for logger datacollector (ScullWM, nicolas-grekas)

This PR was merged into the 3.3-dev branch.

Discussion
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Persist app bootstrapping logs for logger datacollector

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | ?
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #21405
| License       | MIT

Logs generated during the container build are catched by the BufferingLogger with a special flag.

They are persist by the LoggerDataCollector and are available in the logger profiler.
In the profiler toolbar, the "container build" logs increment the current logs counter (even if the container was previously built).

<img width="540" alt="capture d ecran 2017-02-01 a 20 56 40" src="https://cloud.githubusercontent.com/assets/1017746/22523826/0bc12e4a-e8c1-11e6-830f-7f6238ea7423.png">

<img width="1022" alt="capture d ecran 2017-02-01 a 20 57 55" src="https://cloud.githubusercontent.com/assets/1017746/22523859/2c48a698-e8c1-11e6-9bdb-d85f3e692938.png">

The BufferingLogger now require the cachePath and the filesystem to persist a (unique) container build logs.
If the current workflow is ok, I will update the test coverage (actually they fail). Maybe we can display the appDevDebugProjectContainerCompiler.log content in that logger profile.

Commits
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2fd18b5503 [VarDumper] Fine tune dumping log messages
ce3ef6a96e Persist app bootstrapping logs for logger datacollector

Author: fabpot

Resources/config/collectors.xml

@@ -32,6 +32,7 @@
             <tag name="data_collector" template="@WebProfiler/Collector/logger.html.twig" id="logger" priority="300" />
             <tag name="monolog.logger" channel="profiler" />
             <argument type="service" id="logger" on-invalid="ignore" />
+            <argument>%kernel.cache_dir%/%kernel.container_class%</argument>
         </service>
 
         <service id="data_collector.time" class="Symfony\Component\HttpKernel\DataCollector\TimeDataCollector" public="false">