Set compute-feature-enabled.attach_encrypted_volume Tempest option

This allows setting the new option in Tempest for toggling whether
or not the Cinder encrypted volume tests should run.

Depends-On: I48eba7c645cc1c979fd766ae9c05efb00957f787

Related-Bug: #1463525

Change-Id: I9e12f8dc9e3e6b68dc031351cb081ee2bc6e6cbb
diff --git a/lib/tempest b/lib/tempest
index 5ea217f..a84ade2 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -379,6 +379,7 @@
     iniset $TEMPEST_CONFIG compute-feature-enabled preserve_ports True
     # TODO(gilliard): Remove the live_migrate_paused_instances flag when Juno is end of life.
     iniset $TEMPEST_CONFIG compute-feature-enabled live_migrate_paused_instances True
+    iniset $TEMPEST_CONFIG compute-feature-enabled attach_encrypted_volume ${ATTACH_ENCRYPTED_VOLUME_AVAILABLE:-True}
 
     # Network
     iniset $TEMPEST_CONFIG network api_version 2.0