Skip whole test_capi if _testcapi is not present

Author: sobolevn

Lib/test/test_capi/__init__.py

@@ -1,5 +1,10 @@
 import os
-from test.support import load_package_tests
+from test.support import import_helper, load_package_tests
+
+# Do not run the whole directory, if `_testcapi` module is missing.
+# It is assumed that all tests in this directory rely on it.
+import_helper.import_module('_testcapi')
+
 
 def load_tests(*args):
     return load_package_tests(os.path.dirname(__file__), *args)