qemu: add helper function for querying OS info

qemu: add helper function for querying OS info

This function queries the guest operating system information and adds
the returned information to an array of typed parameters with field
names intended to be returned in virDomainGetGuestInfo().

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>