qemuxml2argvtest: add test for remove cpu features

qemuxml2argvtest: add test for remove cpu features

CPU features that always were a no-op in qemu got removed there.
We no more specify them as that would trigger errors and fail to start
qemu. This test ensures that those features really are not rendered into
qemu command line.

Without the related fix this test will trigger and fail like:
 In 'tests/qemuxml2argvdata/cpu-no-removed-features.args':
 Offset 371
 Expect [ ]
 Actual [,-osxsave,-ospke ]

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>