Make cleanup more robust and minor code cleaning in run benchmark script.

Make cleanup more robust and minor code cleaning in run benchmark script.
https://bugs.webkit.org/show_bug.cgi?id=147800

Patch by Dewei Zhu <dewei_zhu@apple.com> on 2015-08-10
Reviewed by Ryosuke Niwa.

Use 'finnaly' block to make sure cleanup code is always executed.

* Scripts/webkitpy/benchmark_runner/benchmark_runner.py:
(built_benchmark):
(built_benchmark.__init__):
(built_benchmark.__enter__):
(built_benchmark.__exit__):
(test_environment):
(test_environment.__init__):
(test_environment.__enter__):
(test_environment.__exit__):
(BenchmarkRunner.__init__):
(BenchmarkRunner.execute):
(BenchmarkRunner._dump):
(BenchmarkRunner._wrap):
(BenchmarkRunner): Deleted.
(BenchmarkRunner._cleanup): Deleted.
* Scripts/webkitpy/benchmark_runner/browser_driver/browser_driver.py:
(BrowserDriver.close_browsers):
(BrowserDriver):
(BrowserDriver.restore_env):
* Scripts/webkitpy/benchmark_runner/http_server_driver/simple_http_server_driver.py:
(SimpleHTTPServerDriver.__init__): We do not actually need to know external ip address for now.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@188237 268f45cc-cd09-0410-ab3c-d52691b4dbfc