Add missing methods to base HardwareManager class

The HardwareManager class was missing a few abstract method
declarations which it is expected to have. Add those.

Change-Id: I1d07b7f08a4fc23929bc09f65b897fdfa0da1770

ironic_python_agent/hardware.py

@@ -90,6 +90,18 @@ class HardwareManager(object):
     def list_network_interfaces(self):
         pass
 
+    @abc.abstractmethod
+    def get_cpus(self):
+        pass
+
+    @abc.abstractmethod
+    def list_block_devices(self):
+        pass
+
+    @abc.abstractmethod
+    def get_memory(self):
+        pass
+
     @abc.abstractmethod
     def get_os_install_device(self):
         pass