bpo-34272: Reorganize C API tests. (GH-8551)

Move some C API tests into Lib/test/test_capi/.
(cherry picked from commit f883b7f8ee)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/test/test_capi/__init__.py

@@ -0,0 +1,5 @@
+import os
+from test.support import load_package_tests
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)

Lib/test/test_capi/__main__.py

@@ -0,0 +1,3 @@
+import unittest
+
+unittest.main('test.test_capi')

Misc/NEWS.d/next/Tests/2018-07-29-15-59-51.bpo-34272.lVX2uR.rst

@@ -0,0 +1 @@
+Some C API tests were moved into the new Lib/test/test_capi/ directory.