[HttpKernel] removed unused variable
Added sleep() workaround for windows php rename bug
merged branch caponica/cache-clear-win-workaround (PR #8767)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #8767).

Discussion
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Added sleep() workaround for windows php rename bug

For more info see links in issue #8766

Commits
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b3c815b Added sleep() workaround for windows php rename bug