Enable to add/remove port to/from a server

This change enables to add/remove a specific port to/from a server using
the new commands:

 openstack server add port <vm> <port>
 openstack server remove port <vm> <port>

Closes-Bug: #1678137
Change-Id: I6ee57df089235ccc1fb9d38316bd484956b1134d

doc/source/command-objects/server.rst

@@ -49,6 +49,26 @@ Add floating IP address to server
 
     Floating IP address (IP address only) to assign to server
 
+server add port
+---------------
+
+Add port to server
+
+.. program:: server add port
+.. code:: bash
+
+    openstack server add port
+        <server>
+        <port>
+
+.. describe:: <server>
+
+    Server to add the port to (name or ID)
+
+.. describe:: <port>
+
+    Port to add to the server (name or ID)
+
 server add security group
 -------------------------
 
@@ -523,6 +543,26 @@ Remove floating IP address from server
 
     Floating IP address (IP address only) to remove from server
 
+server remove port
+------------------
+
+Remove port from server
+
+.. program:: server remove port
+.. code:: bash
+
+    openstack server remove port
+        <server>
+        <port>
+
+.. describe:: <server>
+
+    Server to remove the port from (name or ID)
+
+.. describe:: <port>
+
+    Port to remove from the server (name or ID)
+
 server remove security group
 ----------------------------