Variable added to evaluate "ENABLE_MONASCA" env for 'kolla/horizon'. In
case 'enable_horizon_monasca' is true, 'policy_item' would be called for
Monasca.
Change-Id: Ie9ecb8ab5d4e74af9b83a5b00ccced5b630ab1ed
Implements: blueprint monasca-ui
Signed-off-by: Hamed Bahadorzadeh <h.bahadorzadeh@gmail.com>