Update attach logic in VolumeEncryptionTest

Pick the same logic as volume attach tests have, when after
volume attach server is rebooted to make sure guest OS
recognize new device.

Change-Id: I92098c7d994dc7d85643da29380866a805f4e869
Related-Prod: PROD-21942
diff --git a/barbican_tempest_plugin/tests/scenario/test_volume_encryption.py b/barbican_tempest_plugin/tests/scenario/test_volume_encryption.py
index 51491d4..c7d2577 100644
--- a/barbican_tempest_plugin/tests/scenario/test_volume_encryption.py
+++ b/barbican_tempest_plugin/tests/scenario/test_volume_encryption.py
@@ -16,6 +16,7 @@
 
 from oslo_log import log as logging
 from tempest.common import utils
+from tempest.common import waiters
 from tempest import config
 from tempest.lib import decorators
 from tempest.lib import exceptions as lib_exc
@@ -68,7 +69,8 @@
             if device_name in disks:
                 return
             if int(time.time()) - start >= wait_timeout:
-                message = 'Device %s was not found in %d sec' % wait_timeout
+                message = ('Device %s did not appear in %d sec' % (
+                    device_name, wait_timeout))
                 raise lib_exc.TimeoutException(message)
 
     def attach_detach_volume(self, server, volume, keypair):
@@ -77,6 +79,13 @@
 
         # Write a timestamp to volume
         server_ip = self.get_server_ip(server)
+        self.servers_client.stop_server(server['id'])
+        waiters.wait_for_server_status(self.servers_client, server['id'],
+                                       'SHUTOFF')
+
+        self.servers_client.start_server(server['id'])
+        waiters.wait_for_server_status(self.servers_client, server['id'],
+                                       'ACTIVE')
         self.wait_for_disk(server_ip, keypair,
                            CONF.compute.volume_device_name)
         timestamp = self.create_timestamp(