Stevedore dependency added to Nailgun

Change-Id: If7df4d7cc81e139250d24f919d5039d8a5c45dc2
Merge "Stevedore dependency added to Nailgun"
Install newer yum and yum-utils on precise

Fixes ISO build failure. Apparently the version of yum (and yum-utils)
shipped with precise is unable to handle OSCI repositories metadata.

Change-Id: Icf1b4226b7b6a73da821cdc2fef60372b1b4c9a2
Closes-bug: #1381535