Fix wrong imports in copy-schema-to-ca.py

Some imports were not possible in old versions of IPA. This caused
import exceptions on the script start.

https://fedorahosted.org/freeipa/ticket/6003

Reviewed-By: Petr Spacek <pspacek@redhat.com>

install/share/copy-schema-to-ca.py

@@ -21,7 +21,17 @@ from ipapython import ipautil
 from ipapython.ipa_log_manager import root_logger, standard_logging_setup
 from ipaserver.install.dsinstance import schema_dirname
 from ipalib import api
-from ipaplatform.constants import constants
+
+try:
+    # BE CAREFUL when using the constants module - you need to define all
+    # the constants separately because of old IPA installations
+    from ipaplatform.constants import constants
+    PKI_USER = constants.PKI_USER
+    DS_USER = constants.DS_USER
+except ImportError:
+    # oh dear, this is an old IPA (3.0+)
+    from ipaserver.install.dsinstance import DS_USER   #pylint: disable=E0611
+    from ipaserver.install.cainstance import PKI_USER  #pylint: disable=E0611
 
 try:
     from ipaplatform import services
@@ -52,8 +62,8 @@ def _sha1_file(filename):
 def add_ca_schema():
     """Copy IPA schema files into the CA DS instance
     """
-    pki_pent = pwd.getpwnam(constants.PKI_USER)
-    ds_pent = pwd.getpwnam(constants.DS_USER)
+    pki_pent = pwd.getpwnam(PKI_USER)
+    ds_pent = pwd.getpwnam(DS_USER)
     for schema_fname in SCHEMA_FILENAMES:
         source_fname = os.path.join(ipautil.SHARE_DIR, schema_fname)
         target_fname = os.path.join(schema_dirname(SERVERID), schema_fname)