block: clean temp code and use QemuOpts in block

Temp code are unnecessary now, so clean them and use QemuOpts parser
in block layer.

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>

Conflicts:
	block/sheepdog.c
qapi: query-command-line-options outputs def_value_str

QMP command query-command-line-options shows details information of
parameters, since added def_value_str, also output it in the QMP
command.

v16->v17:
1) add "Since 1.6" tag.
2) rename def_str_value to "default".

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
qemu-option: remove QEMUOptionParameter related functions and struct

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>

Conflicts:
	include/qemu/option.h