Make the "most recent" pubkey first served

And hope it's a protocol 2 key, I really can't think of anything else
outside of asking the user which key to serve at image creation time to
this one ssh key problem

tmcd/Ec2MetaServer.py

@@ -142,7 +142,7 @@ class Ec2MetaHandler(BaseHTTPRequestHandler):
                 "join experiments on experiments.pid=group_membership.pid AND experiments.gid=group_membership.gid "
                 "join reserved on reserved.exptidx=experiments.idx "
                 "join interfaces on reserved.node_id=interfaces.node_id "
-                "where interfaces.ip=%s and user_pubkeys.uid=experiments.expt_swap_uid "
+                "where interfaces.ip=%s and user_pubkeys.uid=experiments.expt_swap_uid ORDER BY idx DESC "
                 "UNION "
                 "select user_pubkeys.uid,user_pubkeys.idx from user_pubkeys "
                 "join group_membership on group_membership.uid = user_pubkeys.uid "
@@ -177,7 +177,7 @@ class Ec2MetaHandler(BaseHTTPRequestHandler):
                 "join experiments on experiments.pid=group_membership.pid AND experiments.gid=group_membership.gid "
                 "join reserved on reserved.exptidx=experiments.idx "
                 "join interfaces on reserved.node_id=interfaces.node_id "
-                "where interfaces.ip=%s and user_pubkeys.uid=experiments.expt_swap_uid) "
+                "where interfaces.ip=%s and user_pubkeys.uid=experiments.expt_swap_uid ORDER BY idx DESC) "
                 "UNION "
                 "(select user_pubkeys.pubkey from user_pubkeys "
                 "join group_membership on group_membership.uid = user_pubkeys.uid "