Make dosep correctly invoke the top level script when doing the multiprocessing fork

[zturner]

Summary

This patch disables the ability to run packages/Python/lldbsuite/test/dotest.py as a standalone script by explicitly erroring out if it detects that to be the case. Then, it fixes up the place where dosep exec's the script to actually exect the main script that we're running from, instead of hardcoding a path to dotest.py, which is now wrong in the presence of being imported as a package.

[tfiala]

Looks good.

We were having trouble running the script from the top level earlier and were directly calling the one that you're disabling. That'll be nice to get the top level one working again.

I hadn't seen the "import main_ as main" trick before. Interesting approach!

[tfiala]

I think this got checked in, right?

packages/Python/lldbsuite/test/dosep.py

     return process_driver.results
 
 
-def process_dir(root, files, test_root, dotest_argv, inferior_pid_events):
+def process_dir(root, files, dotest_argv, inferior_pid_events):
     """Examine a directory for tests, and invoke any found within it."""
     results = []
     for name in files:
-        script_file = os.path.join(test_root, "dotest.py")
+        import __main__ as main
+        script_file = main.__file__
         command = ([sys.executable, script_file] +
                    dotest_argv +
                    ["--inferior", "-p", name, root])

     test_work_items = []
     find_test_files_in_dir_tree(
         test_subdir, lambda testdir, test_files: test_work_items.append([
-            test_subdir, test_files, test_directory, dotest_argv, None]))
+            test_subdir, test_files, dotest_argv, None]))
 
     # Convert test work items into test results using whatever
     # was provided as the test run function.

packages/Python/lldbsuite/test/dotest.py

-#!/usr/bin/env python
-
 """
 A simple testing framework for lldb using python's unit testing framework.
 

     exitTestSuite(failed)
 
 if __name__ == "__main__":
-    run_suite()
+    print(__file__ + " is for use as a module only.  It should not be run as a standalone script.")
+    sys.exit(-1)