[FIX] tests race condition in phanthomjs tests
A deadlock occurs when
- phantomjs_test1 is executedd, enter_test_mode is activated
- console.log('ok') is issued, sigterm is sent to phantomjs_test1 process
- phantomjs_test1 is finished and leave_test_mode restores the registrymanager lock
- phantomjs_test1 process, just before dying, makes a last http request phantomjs_test1_last_request
- phantomjs_test1_last_request thread will wait for the registrymanager lock, when all tests will be completed 
- phantomjs_test2 is run, enter_test_mode is activated
- phantomjs_test2 is reach its end and _wait_remaining_requests is called
- phantomjs_test2 _wait_remaining_requests hangs forever waiting for phantomjs_test1_last_request