Adds qemu packages to ironic's apts

Nodepool images have recently migrated to being built with DIB, resulting
in strange changes in how the package dependency chain works out.  This
explicitly adds required qemu packages to Ironic's apts to avoid some
not being pulled in by package dependencies alone.

Change-Id: I60373ee5ad7445cd54c8c013085b28d82bb0d085
Closes-bug: #1376863
Merge "Adds qemu packages to ironic's apts"