tests: Update RISCV boot tests to use Ubuntu resource

This ubuntu disk image will execute an 'm5 exit' after boot and can
therefore be used to execute "boot exit" tests as part of our
long/nightly tests. These are included in this patch.

Change-Id: Ia5bdb1bfc3d9100b2ea15e23bddb49f7c4faf32d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52089
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
2 files changed