keypairs shouldn't be in LDAP

Keypairs were stored in LDAP for historical reasons (in nova 0.1, LDAP was the only persistent datastore)

Now that we've got a more solid datastore, it would be nice to move them to where the rest of the non-user data resides.

Storing the keys in LDAP added complexity and brittleness to the code (since we had to add a custom LDAP schema, and LDAP seems to throw exceptions 0.5% of the time when we launch instances:

ERROR:root:instance i-1470: Failed to spawn
Traceback (most recent call last):
 File "/srv/cloud/nova/nova/compute/manager.py", line 86, in run_instance
   yield self.driver.spawn(instance_ref)
 File "/usr/local/lib/python2.6/dist-packages/twisted/internet/defer.py", line 821, in _inlineCallbacks
   result = result.throwExceptionIntoGenerator(g)
 File "/usr/local/lib/python2.6/dist-packages/twisted/python/failure.py", line 338, in throwExceptionIntoGenerator
   return g.throw(self.type, self.value, self.tb)
 File "/srv/cloud/nova/nova/virt/libvirt_conn.py", line 217, in spawn
   yield self._create_image(instance, xml)
 File "/usr/local/lib/python2.6/dist-packages/twisted/internet/defer.py", line 823, in _inlineCallbacks
   result = g.send(result)
 File "/srv/cloud/nova/nova/virt/libvirt_conn.py", line 267, in _create_image
   project = manager.AuthManager().get_project(inst['project_id'])
 File "/srv/cloud/nova/nova/auth/manager.py", line 484, in get_project
   with self.driver() as drv:
 File "/srv/cloud/nova/nova/auth/ldapdriver.py", line 82, in __enter__
   self.conn.simple_bind_s(FLAGS.ldap_user_dn, FLAGS.ldap_password)
 File "/usr/lib/python2.6/dist-packages/ldap/ldapobject.py", line 207, in simple_bind_s
   return self.result(msgid,all=1,timeout=self.timeout)
 File "/usr/lib/python2.6/dist-packages/ldap/ldapobject.py", line 436, in result
   res_type,res_data,res_msgid = self.result2(msgid,all,timeout)
 File "/usr/lib/python2.6/dist-packages/ldap/ldapobject.py", line 440, in result2
   res_type, res_data, res_msgid, srv_ctrls = self.result3(msgid,all,timeout)
 File "/usr/lib/python2.6/dist-packages/ldap/ldapobject.py", line 446, in result3
   ldap_result = self._ldap_call(self._l.result3,msgid,all,timeout)
 File "/usr/lib/python2.6/dist-packages/ldap/ldapobject.py", line 96, in _ldap_call
   result = func(*args,**kwargs)
SERVER_DOWN: {'desc': "Can't contact LDAP server"}