[EFL] API unit tests are running extremely slow on the bots
https://bugs.webkit.org/show_bug.cgi?id=104665

Reviewed by Gyuyoung Kim.

Clear HTTP cache files before running the unit tests, which prevents
performance degradation due to so many cache files.

* UIProcess/API/efl/tests/UnitTestUtils/EWK2UnitTestBase.cpp:
(EWK2UnitTest::EWK2UnitTestBase::SetUp):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140348 268f45cc-cd09-0410-ab3c-d52691b4dbfc