[FrameworkBundle] added feedback in cache:clear
[FrameworkBundle] simplified code
feature #9966 added feedback to the cache:clear command (fabpot)

This PR was merged into the 2.5-dev branch.

Discussion
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added feedback to the cache:clear command

simplified version of #9463

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9463
| License       | MIT
| Doc PR        | n/a

"Especially in production it is sometimes critical to know exactly when your cache is cleared or warmed up. Currently cache:clear provides no feedback whats however. As sites get bigger, so become their cache files. Removing old cache files may sometimes even take minutes. Without any feedback from the cache:clear you do not know the current status.

That's why i added more feedback to the cache:clear command that it makes it possible to see when your cache is warmed up and ready to go."

Commits
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f2261da [FrameworkBundle] simplified code
a1f6411 [FrameworkBundle] added feedback in cache:clear