Set barbican host_href param to $SERVICE_HOST on devstack

Default barbican host_href config value has 'localhost' as the host
which will be part of secret_ref uri. On devstack, barbican registers
$SERVICE_HOST as its host in keystone and that doesn't resolve to
localhost on F20 when someone authenticates with keystone.
Pointing barbican host_href to $SERVICE_HOST solves the issue.

Closes-Bug: #1371252
Change-Id: I6269189565b487afaa1330b364e0d6fea2131b55
Merge "Set barbican host_href param to $SERVICE_HOST on devstack"