qemu_command: Separate domain features building into a helper

qemu_command: Separate domain features building into a helper

The qemuBuildMachineCommandLine() function is needlessly long.
Separate out parts that generate arguments based on
domainDef->features[] into
qemuAppendDomainFeaturesMachineParam(). Unfortunately, expected
outputs for some qemuxml2argvdata cases needed to be updated
because the order in which features are generated is changed. But
there's no functional change.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>