Tolerate set_admin_password not implemented.

Allow skipping of password test if this action
is not implemented by the virt driver.

New variable was added to devstack gate in https://review.openstack.org/#/c/10215/1

This will allow the following nova patch to be gated:

https://review.openstack.org/10130

Change-Id: I0ebd34c74bd6a4f0a31fb29f38acdbf060c64617
diff --git a/etc/tempest.conf.tpl b/etc/tempest.conf.tpl
index e6a3891..480d74b 100644
--- a/etc/tempest.conf.tpl
+++ b/etc/tempest.conf.tpl
@@ -72,6 +72,9 @@
 # Cluster: the 'nova' user must have scp access between cluster nodes
 resize_available = %COMPUTE_RESIZE_AVAILABLE%
 
+# Does the compute API support changing the admin password?
+change_password_available = %COMPUTE_CHANGE_PASSWORD_AVAILABLE%
+
 # Level to log Compute API request/response details.
 log_level = %COMPUTE_LOG_LEVEL%