In some cases where we wish to use X86 KVM the 'valid_hosts' field was set to 'constants.supported_hosts'. This can cause problems as the only valid host for an X86 KVM test is X86. This patch fixes this. This fix will likely fix some flakey errors observed in the Nightly tests. Change-Id: Id0a906ca6602c0358ae632cce314769807bf6e07 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58970 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>