Fix the error when monitor calls _is_admin with context not available

Catch the runtime error and return False as the monitor will not have a context and it needs to relocate the host which is reservable - so return false

blazar/plugins/oshosts/host_plugin.py

@@ -660,7 +660,11 @@ def allocation_candidates(self, values):
         return host_ids
 
     def _is_admin(self):
-        ctx = context.current()
+        try:
+            # when monitor calls this will raise an error
+            ctx = context.current()
+        except RuntimeError:
+            return False
         if policy.enforce(ctx, 'admin', {}, do_raise=False):
             return True
         else: