Passing service_protocol in identity-admin relation

Currently indentity-admin relation only passes the following params

service_hostname
service_port
service_username
service_tenant_name
service_region

service_protocol is also required by charms using this relation.
Used the https() function from charmhelpers.contrib.hahelpers.cluster
for this.

Change-Id: I4ae93e2f7a3af4355ec20f68aa05f7d4f11f4ae1