Allow setting qemu process name v2

Set the Linux process name to the name argument specified with name. I find
this useful to see which guests are taking CPU time in top.

This doesn't affect ps, which checks argv[0], but rewriting the
environment uses much more code, so I only used this simple way.

v2: Use separate process= argument, no prefixes.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
