libvirt: host update disable/enable report HTTP 400

When disable/enable host with host-update command, end user will
get HTTP 400 error even if the host was updated(disabled/enabled)
successfully.

The root cause is that after the host was disabled/enabled, nova
api need depend on host status result to check if the host was
disabled or enabled, but libvirt driver did not return host status
to nova api.

Change-Id: I0688134eecb0628b680c8ed01741f00f80eec53f
Closes-Bug: #1251589
Merge "libvirt: host update disable/enable report HTTP 400"