Add support for isa-serial method for qemu-ga on Windows,
Added -p command line parameter for serial port name
specification, e.g. "-p COM15".
Signed-off-by: NMiki Mishael <mmishael@redhat.com>
Signed-off-by: NDmitry Fleytman <dfleytma@redhat.com>

*added default isa-serial path to help output
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>