tests: Migrated 10.linux-boot scons-based test to testlib

tests: Migrated 10.linux-boot scons-based test to testlib

This test has purposely been designed to be easily extendible for future
x86 boot tests. Right now, it only runs two basic Ubuntu boot test
setups.

Change-Id: I81385b5dfc0764af2ec02999eb26e523bd09a595
Issue-on: https://gem5.atlassian.net/browse/GEM5-109
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26324
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>