Set manila::keystone::auth::tenant

Set manila::keystone::auth::tenant

Without setting this parameter, overcloud deploy fails and
'openstack stack failures list overcloud' reveals the
following error:

    Error: Puppet::Type::Keystone_user_role::ProviderOpenstack: Could
not find project with name [services] and domain [Default]
    Error:
/Stage[main]/Manila::Keystone::Auth/Keystone::Resource::Service_identity[manilav2]/Keystone_user_role[manilav2@services]:
Could not evaluate: undefined method `[]' for nil:NilClass

When we set manila::keystone::auth::tenant to 'service', analogous
to cinder, nova, etc., the overcloud deploy completes successfully.

Change-Id: I996ac2ff602c632a9f9ea9c293472a6f2f92fd72