Add checks for some NIC hotplug related features added in qemu-0.10.0

Add checks for some NIC hotplug related features added in qemu-0.10.0

Add QEMUD_CMD_FLAG_NET_NAME to indicate that '-net ...,name=foo' is
supported and QEMUD_CMD_FLAG_HOST_NET_ADD to indicate that the
'host_net_add' monitor command is available.

Set both these flags if the qemu version is greater than 0.10.0.
Checking via the '-help' output would not work for the monitor command
and even for the command line arg, it would be quite fragile.

* src/qemu_conf.h: add new flags as aliases of QEMUD_CMD_FLAG_0_10

* src/qemu_conf.c: set QEMUD_CMD_FLAG_0_10 for versions >= 0.10.0

* tests/qemuhelptest.c: set QEMUD_CMD_FLAG_0_10 for the appropriate
  qemu versions