Import heartbeat_interval opt in API
Import heartbeat_interval opt in API

The API for /v1/drivers needs to read the conductor.heartbeat_timeout
option from ironic.conductor.manager in order to get the list of
active conductor drivers from the database.

Change-Id: If6abd41ac01b3704bbdda0212d07abcaa0339ef9
Closes-bug: 1258207

ionutbalutoiu/ironic,NaohiroTamura/ironic,bacaldwell/ironic,ramineni/myironic,redhat-openstack/ironic,pshchelo/ironic,rdo-management/ironic,naterh/ironic,debayanray/ironic_backup,openstack/ironic,naototty/vagrant-lxc-ironic,hpproliant/ironic,SauloAislan/ironic,rackerlabs/ironic,supermari0/ironic,froyobin/ironic,naototty/vagrant-lxc-ironic,dims/ironic,dims/ironic,ionutbalutoiu/ironic,devananda/ironic,NaohiroTamura/ironic,pshchelo/ironic,SauloAislan/ironic,Tehsmash/ironic,openstack/ironic,faizan-barmawer/openstack_ironic,bacaldwell/ironic,varunarya10/ironic,JioCloud/ironic,Tan0/ironic