server-del: perform full master removal in managed topology

This patch implements most of the del_master_managed() functionality as a part
of `server-del` command.

`server-del` nows performs these actions:
  * check topology connectivity
  * check that at least one CA/DNS server and DNSSec masters are left
    after removal
  * cleanup all LDAP entries/attributes exposing information about the master
  * cleanup master DNS records
  * remove master and service principals
  * remove master entry from LDAP
  * check that all segments pointing to the master were removed

  `server-del` now accepts the following options:
  * `--force`: force master removal even if it doesn't exist
  * `--ignore-topology-disconnect`: ignore errors arising from disconnected
    topology before and after master removal
  * `--ignore-last-of-role`: remove master even if it is last DNS server,
    and DNSSec key master. The last CA will *not* be removed regardless of
    this option.

https://fedorahosted.org/freeipa/ticket/5588

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

ipaclient/plugins/server.py

@@ -0,0 +1,17 @@
+#
+# Copyright (C) 2016 FreeIPA Contributors see COPYING for license
+#
+
+from ipaclient.frontend import MethodOverride
+from ipalib import _
+from ipalib.plugable import Registry
+
+register = Registry()
+
+
+@register(override=True)
+class server_del(MethodOverride):
+    def interactive_prompt_callback(self, kw):
+        self.api.Backend.textui.print_plain(
+            _("Removing %(servers)s from replication topology, "
+              "please wait...") % {'servers': ', '.join(kw['cn'])})