Global Catalog: remove DNS record only when last instance is removed

During the GC uninstallation, all the GC-related DNS records are
deleted, even though another master may be providing the GC role.
Delete the records only when the last instance of GC is removed.

If the deletion fails for an unexpected reason, do not raise the
exception but continue the uninstallation after logging the error.

Fixes: #63

ipaserver/install/gcinstance.py

@@ -46,6 +46,7 @@
     is_ds_running,
 )
 from ipaserver.install.adtrustinstance import make_netbios_name
+from ipaserver.servroles import ENABLED
 from ipapython.dnsutil import DNSName
 from lib389 import DirSrv
 from lib389.idm.ipadomain import IpaDomain
@@ -755,6 +756,10 @@ def __remove_gc_dns_records(self):
                 pass
             except IPADomainIsNotManagedByIPAError:
                 pass
+            except Exception as e:
+                # print an error msg but do not prevent uninstallation
+                logger.error("Failed to delete DNS record for GC %s: %s",
+                             record[0].to_text(), e)
 
     def apply_updates(self):
         # Question: do we need to support loading schema files from
@@ -793,7 +798,15 @@ def uninstall(self):
                          "service principal manually.")
         else:
             # Remove the DNS records for global catalog
-            self.__remove_gc_dns_records()
+            # if it was the last instance
+            try:
+                api.Command.server_role_find(
+                    role_servrole=u'Global Catalog server',
+                    status=ENABLED
+                )
+            except errors.EmptyResult:
+                # This server was the last GC, delete DNS records
+                self.__remove_gc_dns_records()
 
             # Remove the service container entry
             self.ldap_remove_service_container(self.serverid, api.env.host,