add spec test for step poweroff
add spec test for step poweroff

Change-Id: I1dfce20b5e3daf2964389409464a45c16d1159ce

wcamarao/bosh-vcloud-cpi-release,cloudfoundry-incubator/bosh-vcloud-cpi-release,cloudfoundry-incubator/bosh-vcloud-cpi-release,wcamarao/bosh-vcloud-cpi-release,wcamarao/bosh-vcloud-cpi-release,cloudfoundry-incubator/bosh-vcloud-cpi-release