Import fixes from Nova scheduler reviews

Import fixes from the Nova scheduler driver review, based upon
revision 4 of https://review.openstack.org/#/c/103165

- create BaseBaremetalHostManager class
- import and refactor the BaremetalHostManager
- refactor IronicHostManager
- minor updates to ExactMatch filters

Note that this change also adds back in copyright notices from
baremetal_host_manager to the ironic_host_manager to reflect
the common heritage of the code.

Change-Id: Iab0d0f1c05474bf341828a2e5aba95715bf71d82
Merge "Import fixes from Nova scheduler reviews"