qemu-option: warn for short-form boolean options

qemu-option: warn for short-form boolean options

Options such as "server" or "nowait", that are commonly found in -chardev,
are sugar for "server=on" and "wait=off".  This is quite surprising and
also does not have any notion of typing attached.  It is even possible to
do "-device e1000,noid" and get a device with "id=off".

Deprecate it and print a warning when it is encountered.  In general,
this short form for boolean options only seems to be in wide use for
-chardev and -spice.

Signed-off-by: Paolo Bonzini <[email protected]>