remove nsenter from warden-ci
remove nsenter from warden-ci

Signed-off-by: Simon Leung <23f08a50fbaf82c4ecfae6738d41887b087c2e71@us.ibm.com>

georgethebeatle/diego-dockerfiles,cloudfoundry-incubator/diego-dockerfiles,georgethebeatle/diego-dockerfiles,cloudfoundry-incubator/diego-dockerfiles