[8.0] Reboot procedure fixed

Added the workaround to avoid the thin pool exhaustion probably caused
by the issue moby/moby#3182

Change-Id: I2edc74189872754383bf9a1f3215490d46e38b27

fuelweb_test/models/environment.py

@@ -675,6 +675,15 @@ def admin_install_updates(self):
         )
         logger.info('Containers terminated')
 
+        # Working around the bug https://github.com/docker/docker/issues/3182
+        logger.info('Removing docker images')
+        self.ssh_manager.execute_on_remote(
+            ip=self.admin_node_ip,
+            cmd='docker rmi -f $(docker images -q)',
+            err_msg='Unable to remove images'
+        )
+        logger.info('Images removed')
+
         logger.info('Searching for updates..')
         update_command = 'yum clean expire-cache && ' \
                          'yum update -y 2>>/var/log/yum-update-error.log'