Ignore stderr in cpi executable tests
Ignore stderr in cpi executable tests

[#100464054](https://www.pivotaltracker.com/story/show/100464054)

Signed-off-by: Edwin Xie <6bc24e9c160281972837d9e13287696d26612564@pivotal.io>

loewenstein/bosh-openstack-cpi-release,loewenstein/bosh-openstack-cpi-release,voelzmo/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,voelzmo/bosh-openstack-cpi-release,voelzmo/bosh-openstack-cpi-release,loewenstein/bosh-openstack-cpi-release