Run sideways ironic greande only on juno branches

This ironic grenade job is meant to test sideways migration within
the Juno release.  The nova code required has been dropped from
master and it will now only run against Juno.  Limit it to run only
against (proposed/stable)/juno.

Change-Id: Ibbdb547269e7bda78e2514dc8957a0cd9b1c7dae
Merge "Run sideways ironic greande only on juno branches"