The two functions work_on_disk and create_config_drive_partition contain
a substantial part of the deployment logic. Previously we placed them in
ironic-lib for re-using on the conductor side in the iSCSI deploy
interface. Since the iSCSI deploy is going away, we can move this code
to ironic-python-agent to simplify maintenance.
Imports code from ironic_lib commit 9fb5be348202f4854a455cd08f400ae12b99e1f2.
Change-Id: I6cbcd81533f135208b57746cb0e33ffdfaf94eee
