QemuOpts: add qemu_opt_get_*_del functions for replace work

QemuOpts: add qemu_opt_get_*_del functions for replace work

Add qemu_opt_get_del, qemu_opt_get_bool_del, qemu_opt_get_number_del and
qemu_opt_get_size_del to replace the same handling of QEMUOptionParameter
(get and delete).

Several drivers are coded to parse a known subset of options, then
remove them from the list before handing all remaining options to a
second driver for further option processing.  get_*_del makes it easier
to retrieve a known option (or its default) and remove it from the list
all in one action.

Share common helper function:

For qemu_opt_get_bool/size/number, they and their get_*_del counterpart
could share most of the code except whether or not deleting the opt from
option list, so generate common helper functions.

For qemu_opt_get and qemu_opt_get_del, keep code duplication, since
1. qemu_opt_get_del returns malloc'd memory while qemu_opt_get returns
in-place memory
2. qemu_opt_get_del returns (char *), qemu_opt_get returns (const char *),
and could not change to (char *), since in one case, it will return
desc->def_value_str, which is (const char *).

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
Signed-off-by: Chunyan Liu <cyliu@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>