TestRunner initial refactor

Preparation for sharing more code between deopt fuzzer and normal test runner.

Bug: v8:6917
Change-Id: Id8022c7597544ffddf5d1b0a0d73bb4a9d163fc3
Reviewed-on: https://chromium-review.googlesource.com/715417
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48521}

tools/testrunner/base_runner.py

+# Copyright 2017 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+import os
+import sys
+
+
+# Add testrunner to the path.
+sys.path.insert(
+  0,
+  os.path.dirname(
+    os.path.dirname(os.path.abspath(__file__))))
+
+
+class BaseTestRunner(object):
+  def __init__(self):
+    pass
+
+  def execute(self):
+    return self._do_execute()
+
+  def _do_execute(self):
+    raise NotImplementedError()