Updates to QEMU builder - Fix -redir and machine type issues

-redir option should not be used anymore, use netdev to pass hostfwd options instead
-machine type option 'pc-1.0' is not supported on some platforms (namely RHEL) and is often just a alias to 'pc-1.0' anyway. Changing this to just 'pc' allows better out of the box behavior.

SSH min/max ports if set to the same number cause a Golang panic.
Fixed using previous code @mitchellh wrote for another packer builder for the same issue.