Improve the get metadata logic

In case the metadata service is not found, cloudbase-init
will now continue on running, instead of throwing an exception,
thus avoiding infinite loops caused by the 'configure_host'.

Change-Id: Id7ae33817c1ec8f3a7366825ab9bcc05997477db
Closes-Bug: #1643921

cloudbaseinit/exception.py

@@ -30,6 +30,13 @@ class ServiceException(Exception):
     pass
 
 
+class MetadaNotFoundException(CloudbaseInitException):
+
+    """Exception thrown in case no metadata service is found."""
+
+    pass
+
+
 class CertificateVerifyFailed(ServiceException):
 
     """The received certificate is not valid.

cloudbaseinit/init.py

@@ -18,6 +18,7 @@ import sys
 from oslo_log import log as oslo_logging
 
 from cloudbaseinit import conf as cloudbaseinit_conf
+from cloudbaseinit import exception
 from cloudbaseinit.metadata import factory as metadata_factory
 from cloudbaseinit.osutils import factory as osutils_factory
 from cloudbaseinit.plugins.common import base as plugins_base
@@ -134,7 +135,12 @@ class InitManager(object):
                 plugins_base.PLUGIN_STAGE_PRE_METADATA_DISCOVERY)
 
         if not (reboot_required and CONF.allow_reboot):
-            service = metadata_factory.get_metadata_service()
+            try:
+                service = metadata_factory.get_metadata_service()
+            except exception.MetadaNotFoundException:
+                LOG.error("No metadata service found")
+                service = None
+        if service:
             LOG.info('Metadata service loaded: \'%s\'' %
                      service.get_name())
 

cloudbaseinit/metadata/factory.py

@@ -34,4 +34,4 @@ def get_metadata_service():
         except Exception as ex:
             LOG.error("Failed to load metadata service '%s'" % class_path)
             LOG.exception(ex)
-    raise exception.CloudbaseInitException("No available service found")
+    raise exception.MetadaNotFoundException("No available service found")