Do not filter with empty alarm id
Do not filter with empty alarm id

Submitting filter form with empty
alarm ID resulted in critical error
in horizon (error in template rendering).

With this commit filter form goes back to
alarms table unless alarm ID is actually set in form.
This is the same behaviour as in filtering based on
dimensions and metric name.

Change-Id: I0e286f0350f5093f455823ded76ed7d179beeb20

openstack/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,openstack/monasca-ui