devstack: add missing variables for ironic-python-agent-builder
devstack: add missing variables for ironic-python-agent-builder

The ones for ironic-python-agent itself are defined in devstack.
This changes adds similar variables for ironic-python-agent-builder
and migrates the ironic-python-agent ones here to avoid confusion.

Change-Id: Ic7eef9c8741ec2900401556f4053a4749b652d7c

openstack/ironic,openstack/ironic