Implement IPMI sub-driver for baremetal compute

This patch implements only the IPMI power manager for baremetal nova
compute. Documentation will come in a separate patch.

blueprint general-bare-metal-provisioning-framework

Change-Id: I60ccfbf963d7bbf6f840e627396601b7bba80e7f
Merge "Implement IPMI sub-driver for baremetal compute"