Use namespace-aware meta importer for ipaplatform

Instead of symlinks and build-time configuration the ipaplatform module
is now able to auto-detect platforms on import time. The meta importer
uses the platform 'ID' from /etc/os-releases. It falls back to 'ID_LIKE'
on platforms like CentOS, which has ID=centos and ID_LIKE="rhel fedora".

The meta importer is able to handle namespace packages and the
ipaplatform package has been turned into a namespace package in order to
support external platform specifications.

https://fedorahosted.org/freeipa/ticket/6474

Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

pypi/test_placeholder.py

@@ -9,13 +9,14 @@ import pytest
 
 @pytest.mark.parametrize("modname", [
     # placeholder packages raise ImportError
-    'ipaplatform',
     'ipaserver',
     'ipatests',
     # PyPI packages do not have install subpackage
     'ipaclient.install',
     'ipalib.install',
     'ipapython.install',
+    # override module should not be shipped in wheels
+    'ipaplatform.override',
 ])
 def test_fail_import(modname):
     try:
@@ -29,6 +30,7 @@ def test_fail_import(modname):
 @pytest.mark.parametrize("modname", [
     'ipaclient',
     'ipalib',
+    'ipaplatform',
     'ipapython',
 ])
 def test_import(modname):