Fix issue starting nova-compute w/ XenServer

In a fresh-install environment, nova-compute will fail to start
due to missing record in compute_nodes table. I have moved the
db update to be included in the update_available_resources function.

Fixes bug 942893

Change-Id: I4b4f6a493ef0bbe81224c7408d0985e14fa9f1bc

nova/virt/xenapi_conn.py

@@ -181,8 +181,6 @@ def __init__(self, url, user, pw):
         self._initiator = None
         self._pool = pool.ResourcePool(self._session)
 
-        self._capture_dom0_hostname()
-
     @property
     def host_state(self):
         if not self._host_state:
@@ -196,22 +194,6 @@ def init_host(self, host):
         #e.g. to do session logout?
         pass
 
-    def _capture_dom0_hostname(self):
-        """Find dom0's hostname and log it to the DB."""
-        ctxt = context.get_admin_context()
-        service = db.service_get_by_host_and_topic(ctxt, FLAGS.host, "compute")
-
-        try:
-            compute_node = db.compute_node_get_for_service(ctxt, service["id"])
-        except TypeError:
-            return
-
-        host_stats = self.get_host_stats()
-
-        db.compute_node_update(ctxt, compute_node["id"],
-                {"hypervisor_hostname": host_stats["host_hostname"]},
-                auto_adjust=False)
-
     def list_instances(self):
         """List VM instances"""
         return self._vmops.list_instances()
@@ -429,6 +411,7 @@ def update_available_resource(self, ctxt, host):
                'local_gb_used': used_disk_gb,
                'hypervisor_type': 'xen',
                'hypervisor_version': 0,
+               'hypervisor_hostname': host_stats['host_hostname'],
                'service_id': service_ref['id'],
                'cpu_info': host_stats['host_cpu_info']['cpu_count']}