minor updates to aurora-build.sh
minor updates to aurora-build.sh

Ensure `apt-get update` is run before attempting to install packages
and remove a redundant `else` statement.
rji/mesos-in-action-code-samples,rji/mesos-in-action-code-samples,rji/mesos-in-action-code-samples,rji/mesos-in-action-code-samples