Perform kernel upgrades on new Ubuntu servers.

* install_jenkins_slave.sh: Perform a dist-upgrade on Ubuntu
servers, similar to install_puppet.sh.

* install_puppet.sh: Change from upgrade to dist-upgrade so kernels
will also be included in the initial package upgrade step.

Change-Id: Ia39c37f75cc411ce92b1deb5125fa0c5c6e6db35
Reviewed-on: https://review.openstack.org/30388
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins