Install sbcl on slaves

This is a Common Lisp interpreter that will be used by
stackforge/cl-openstack-client to run its unit tests.

Change-Id: I290833ee9ee846eaf4072f8339aa6f54a409681e
Signed-off-by: Julien Danjou <julien@danjou.info>
Reviewed-on: https://review.openstack.org/33440
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins