Migrate 'multimanager' to 'swarm'

It's easier to say 'swarm' and conveys the sense without confusion
of 'cluster' mode.

confluent_server/confluent/swarm/invites.py

@@ -0,0 +1,55 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2018 Lenovo
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This handles the process of generating and tracking/validating invites
+
+import base64
+import hashlib
+import hmac
+import os
+pending_invites = {}
+
+def create_server_invitation(servername):
+    invitation = os.urandom(66)
+    pending_invites[servername] = invitation
+    return base64.b64encode(invitation)
+
+def create_client_proof(invitation, mycert, peercert):
+    return hmac.new(invitation, peercert + mycert, hashlib.sha256).digest()
+
+def check_server_proof(invitation, mycert, peercert, proof):
+    validproof = hmac.new(invitation, mycert + peercert, hashlib.sha256
+                          ).digest()
+    return proof == validproof
+
+def check_client_proof(servername, mycert, peercert, proof):
+    invitation = pending_invites[servername]
+    validproof = hmac.new(invitation, mycert + peercert, hashlib.sha256
+                          ).digest()
+    if proof == validproof:
+        # We know that the client knew the secret, and that it measured our
+        # certificate, and thus calling code can bless the certificate, and
+        # we can forget the invitation
+        del pending_invites[servername]
+        # We now want to prove to the client that we also know the secret,
+        # and that we measured their certificate well
+        # Now to generate an answer...., reverse the cert order so our answer
+        # is different, but still proving things
+        return hmac.new(invitation, peercert + mycert, hashlib.sha256
+                          ).digest()
+    # The given proof did not verify the invitation
+    return False
+