Use xenial instead of trusty for bats stemcell
Use xenial instead of trusty for bats stemcell

Co-authored-by: Rebecca Putinski <1769705669056ac7df0c2658a01b1e2790d3ae82@pivotal.io>

cloudfoundry-incubator/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release,cloudfoundry-incubator/bosh-azure-cpi-release,cloudfoundry-incubator/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release