add def_value_str and use it in qemu_opts_print

qemu_opts_print has no user now, so can re-write the function safely.

qemu_opts_print will be used while using "qemu-img create", it will
produce the same output as previous code.

The behavior of this function has changed:

1. Print every possible option, whether a value has been set or not.
2. Option descriptors may provide a default value.
3. Print to stdout instead of stderr.

Previously the behavior was to print every option that has been set.
Options that have not been set would be skipped.

v11->v12
1) make def_value_str become the real default value string in opt_set
function.

v10->v11:
1)  print all values that have actually been assigned while accept-any
cases.

v7->v8:
1) print "elements => accept any params" while opts_accepts_any() ==
true.
2) since def_print_str is the default value if an option isn't set,
so rename it to def_value_str.

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
Create four QemuOptsList related functions

This patch will create 4 functions, count_opts_list, qemu_opts_append,
qemu_opts_free and qemu_opts_print_help, they will be used in following
commits.

v11->v12:
1) renmae functions.
2) fix loop styles and code styles.
3) qemu_opts_apend will not return NULL now.
4) merge_lists value is from arguments in qemu_opts_append.

v6->v7:
1) Fix typo.

v5->v6:
1) allocate enough space in append_opts_list function.

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
Use QemuOpts support in block layer

This patch will use QemuOpts related functions in block layer, add
a member bdrv_create_opts to BlockDriver struct, it will return
a QemuOptsList pointer, which includes the image format's create
options.

And create options's primary consumer is block creating related
functions, so modify them together.

v11->v12:
1) create functions, such as qemu_opt_get_del  and qemu_opt_replace_set.
These functions works like origin code.
2) use QEMU_OPT_SIZE, not QEMU_OPT_NUMBER.
3) in bdrv_create, if opts is NULL, will create an empty one, so can
discard if(opts) code safely.

v10->v11:
1) qed.h move QED_DEFAULT_CLUSTER_SIZE from enum to macro, or
qemu_opts_print produce un-expanded cluster_size.
2) In qcow2.c and qcow.c, bdrv_create_file(filename, NULL), NULL ->
opts,
or while using protocol, there will be an error.

v8->v9:
1) add qemu_ prefix to gluster_create_opts.
2) fix bug: bdrv_gluster_unix and bdrv_gluster_rdma should also be
   converted.

v7->v8:
1) rebase to upstream source tree.
2) add gluster.c, raw-win32.c, and rbd.c.

v6->v7:
1) use osdep.h:stringify(), not redefining new macro.
2) preserve TODO comment.
3) fix typo. BLOCK_OPT_ENCRYPT->BLOCK_OPT_STATIC.
4) initialize disk_type even when opts is NULL.

v5->v6:
1) judge if opts == NULL in block layer create functions.
2) use bdrv_create_file(filename, NULL) in qcow_create and cow_create
funtion.
3) made more readable while using qemu_opt_get_number.

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