Switch ironic-multitest to agent_ssh
Switch ironic-multitest to agent_ssh

Switch initial devstack setup for ironic-multitest job to agent_ssh
driver. Configuring devstack with agent_* driver allow to execute
tests for nodes with pxe_* driver, but not vice versa since agent_*
reqiures SWIFT_TEMP_URLS to be configured.

Change-Id: I54a920eaafd69a0b6e06d83a9374fcd6319cf96a

Tesora/tesora-project-config,openstack-infra/project-config,Tesora/tesora-project-config,openstack-infra/project-config