pylint_plugins: add forbidden import checker

Add new pylint AST checker plugin which implements a check for imports
forbidden in IPA. Which imports are forbidden is configurable in pylintrc.

Provide default forbidden import configuration and disable the check for
existing forbidden imports in our code base.

Reviewed-By: Martin Basti <mbasti@redhat.com>

ipaplatform/base/services.py

@@ -93,11 +93,13 @@ class PlatformService(object):
     """
 
     def __init__(self, service_name, api=None):
+        # pylint: disable=ipa-forbidden-import
+        import ipalib  # FixMe: break import cycle
+        # pylint: enable=ipa-forbidden-import
         self.service_name = service_name
         if api is not None:
             self.api = api
         else:
-            import ipalib  # FixMe: break import cycle
             self.api = ipalib.api
             warnings.warn(
                 "{s.__class__.__name__}('{s.service_name}', api=None) "

ipaplatform/debian/services.py

@@ -166,7 +166,9 @@ def debian_service_class_factory(name, api=None):
 
 class DebianServices(base_services.KnownServices):
     def __init__(self):
+        # pylint: disable=ipa-forbidden-import
         import ipalib  # FixMe: break import cycle
+        # pylint: enable=ipa-forbidden-import
         services = dict()
         for s in base_services.wellknownservices:
             services[s] = self.service_class_factory(s, ipalib.api)

ipaplatform/redhat/services.py

@@ -253,7 +253,9 @@ def redhat_service_class_factory(name, api=None):
 
 class RedHatServices(base_services.KnownServices):
     def __init__(self):
+        # pylint: disable=ipa-forbidden-import
         import ipalib  # FixMe: break import cycle
+        # pylint: enable=ipa-forbidden-import
         services = dict()
         for s in base_services.wellknownservices:
             services[s] = self.service_class_factory(s, ipalib.api)

ipaplatform/redhat/tasks.py

@@ -50,7 +50,9 @@ from ipaplatform.paths import paths
 from ipaplatform.redhat.authconfig import RedHatAuthConfig
 from ipaplatform.base.tasks import BaseTaskNamespace
 
+# pylint: disable=ipa-forbidden-import
 from ipalib.constants import IPAAPI_USER
+# pylint: enable=ipa-forbidden-import
 
 _ffi = FFI()
 _ffi.cdef("""
@@ -235,8 +237,10 @@ class RedHatTaskNamespace(BaseTaskNamespace):
             return True
 
     def insert_ca_certs_into_systemwide_ca_store(self, ca_certs):
+        # pylint: disable=ipa-forbidden-import
         from ipalib import x509  # FixMe: break import cycle
         from ipalib.errors import CertificateError
+        # pylint: enable=ipa-forbidden-import
 
         new_cacert_path = paths.SYSTEMWIDE_IPA_CA_CRT