SSHPower driver support VMware ESXi

Support for VMware ESXi is being added to the Nova baremetal driver.
https://review.openstack.org/#/c/58940/5
This needs to be ported to Ironic's SSHPower driver.

Change-Id: I89635d13114d0a778fc312884099c61a68fc1f8e
Closes-Bug: #1260414