Remove thirdparty/unittest2 from webkitpy and require python2.7.

Tools/Scripts/webkitpy/layout_tests/port/driver_unittest.py

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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.system.systemhost_mock import MockSystemHost
 
 from webkitpy.layout_tests.port import Port, Driver, DriverOutput
 from webkitpy.layout_tests.port.server_process_mock import MockServerProcess
 
 # FIXME: remove the dependency on TestWebKitPort
 from webkitpy.layout_tests.port.port_testcase import TestWebKitPort
 
 from webkitpy.tool.mocktool import MockOptions
@@ skipping 194 matching lines @@
         last_tmpdir = port._filesystem.last_tmpdir
         driver._start(True, [])
         self.assertFalse(port._filesystem.isdir(last_tmpdir))
 
     def test_start_actually_starts(self):
         port = TestWebKitPort()
         port._server_process_constructor = MockServerProcess
         driver = Driver(port, 0, pixel_tests=True)
         driver.start(True, [], None)
         self.assertTrue(driver._server_process.started)